GM Chevy Mid-Size Cars 1964-1988 Repair Guide

Carburetor

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Idle mixture and speed adjustments are critical aspects of exhaust emission control. It is important that all tune-up instructions be carefully followed to ensure satisfactory engine performance and minimum exhaust pollution. The different combinations of emission system applications on the various engines have resulted in a great variety of tune-up specifications. See the Tune-Up Specifications chart at the beginning of this section. Beginning in 1968, all models should have a decal conspicuously placed in the engine compartment that gives tune-up specifications. Because this label will often contain changes to specification made during production, it's information should always supersede that on the specification chart.

When adjusting a carburetor with two idle mixture screws, adjust them alternately and evenly, unless otherwise stated.

ADJUSTING THE IDLE SPEED AND MIXTURE



See Figures 1, 2, 3, 4 and 5

In the following adjustment procedures the term lean roll means turning the mixture adjusting screws in (clockwise) from optimum setting to obtain an obvious drop in engine speed (usually 20 rpm). See Fuel System for additional adjustments and specifications for Carter and Rochester carburetors.

1964-66

Turn the idle screw(s) slightly in to seat, and then back out 1 1 / 2 turns (3 when equipped with A.I.R.). Do not turn the idle mixture screws tightly against their seats or you could damage the screws. With the engine idling at operating temperature (air cleaner installed, preheater valve and choke valve wide open), adjust the idle speed to specification (automatic transmission in Drive; manual in Neutral).

Adjust the mixture screw to obtain the highest steady idle speed, then adjust the idle speed screw to the specified rpm. Adjust the mixture screw in to obtain a 20 rpm drop, then back the screw out 1 / 4 turn. Repeat this operation on the second mixture, if so equipped. Readjust the idle speed screw as necessary until the specified rpm is reached.

1967 Without Air

Adjust with the air cleaner removed.

  1. Remove the air cleaner.
  2.  
  3. Connect a tachometer and vacuum gauge to the engine, set the parking brake, and place the transmission in Neutral.
  4.  
  5. Turn in the idle mixture screws until they gently seat, then back out 1 1 / 2 turns.
  6.  
  7. Start the engine and allow it to come to the normal operating temperature. Make sure the choke is fully open, then adjust the idle speed screw to obtain the specified idle speed (automatic in Drive, manual in Neutral).
  8.  
  9. Adjust the idle mixture screw(s) to obtain the highest steady vacuum at the specified idle speed, except for the Rochester BV. For this carburetor, adjust the idle mixture screw out 1 / 4 turn from lean drop-off (the point where a 20-30 rpm drop is achieved by leaning the mixture).
  10.  

On carburetors having a hot idle compensator valve (A/C models), hold the brass valve down with a pencil while making the mixture adjustment.

  1. Repeat Steps four and five as necessary.
  2.  
  3. Turn off the engine, remove the gauges, and install the air cleaner.
  4.  

1967 With Air

Adjust with the air cleaner removed.

During this adjustment, air conditioning should be turned off on 327 and 350 cu. in. engines.

  1. Remove the air cleaner.
  2.  
  3. Connect a tachometer and a vacuum gauge to the engine, set the parking brake, and place the transmission in Neutral.
  4.  
  5. Turn in the idle mixture screw(s) until they gently seat, then back them out three turns.
  6.  
  7. Start the engine and allow it to reach normal operating temperature. Make sure the choke is fully open, then adjust the idle speed screw(s) to obtain the specified idle speed (automatic in Drive, manual in Neutral).
  8.  
  9. Turn the idle mixture screw(s) clockwise (in) to the point where a 20-30 rpm drop in the speed is achieved; this is the lean drop off point. Back out the screws 1 / 4 turn from this point.
  10.  
  11. Repeat Steps four and five if necessary.
  12.  
  13. Turn off the engine, remove the gauges, and install the air cleaner.
  14.  

1968-69

Adjust with the air cleaner installed.

Turn off the air conditioner (if applicable) unless you car is a 1968 model with the 6-cylinder engine and automatic transmission. These cars should have the air conditioner turned on when setting the idle.

  1. Turn in the idle mixture screw(s) until they seat gently, then back them out three turns.
  2.  
  3. Start the engine and allow it to reach operating temperature. Make sure the choke is fully open and the preheater valve is open, then adjust the idle speed screw to obtain the specified idle speed (automatic in Drive, manual in Neutral).
  4.  
  5. Adjust the idle mixture screw(s) to obtain the highest steady idle speed, then readjust the idle speed screw to obtain the specified speed. On cars with an idle stop solenoid adjust as follows:
    1. Adjust the idle speed to 500 RPM (6 cylinder) or 600 rpm (1968 V8) by turning the hex on the solenoid plunger. Refer to the tune-up decal in the engine compartment for 1969 idle speeds.
    2.  
    3. Disconnect the wire at the solenoid. This allows the throttle lever to seat against the idle screw.
    4.  
    5. Adjust the idle screw to obtain 400 rpm (1968), then reconnect the wire. On 1969 models, adjust the idle as specified on the tune-up decal in the engine compartment.
    6.  

  6.  
  7. Adjust one mixture screw to obtain a 20 rpm drop in idle speed, and back out the screw 1 / 4 turn from this point.
  8.  
  9. Repeat Steps three and four for the second mixture screw (if so equipped).
  10.  
  11. Readjust the idle speed to obtain the specified idle speed.
  12.  

1970 Initial Adjustments

Adjust with the air cleaner installed.

  1. Disconnect the fuel tank line from the vapor canister (EEC).
  2.  
  3. Connect a tachometer to the engine, start the engine and allow it to reach operating temperature. Make sure the choke and preheater valves are fully open.
  4.  
  5. Turn off the air conditioner and set the parking brake. Disconnect and plug the distributor vacuum line.
  6.  
  7. Make the following adjustments:
  8.  

6-CYLINDER 250 ENGINE
  1. Turn in the mixture screw until it gently seats, then back out the screw four turns.
  2.  
  3. Adjust the solenoid screw to obtain 830 rpm for manual transmissions (in Neutral) or 630 rpm for automatic transmission (in Drive).
  4.  
  5. Adjust the mixture screw to obtain 750 rpm for manual transmissions (in Neutral) or 600 rpm for automatic transmissions (in Drive).
  6.  
  7. Disconnect the solenoid wire and set the idle speed to 400 rpm, then reconnect it.
  8.  
  9. Reconnect the distributor vacuum line.
  10.  

V8-307 & 400 ENGINES
  1. Turn in the mixture screws until they seat gently, then back them out four turns.
  2.  
  3. Adjust the carburetor idle speed screw to obtain 800 rpm for manual transmissions (in Neutral), or adjust the solenoid screw to obtain 630 rpm for automatic transmissions (in Drive).
  4.  
  5. Adjust both mixture screws equally inward to obtain 700 rpm for manual transmissions, 600 rpm for automatic transmissions (in Drive).
  6.  
  7. On cars with automatic transmissions, disconnect the solenoid wire, set the carburetor idle screw to obtain 450 rpm and reconnect the solenoid.
  8.  
  9. Reconnect the distributor vacuum line.
  10.  

V8-350 (250 HP) ENGINE
  1. Turn in the mixture screws until they gently seat, then back them out four turns.
  2.  
  3. Adjust the solenoid screw to obtain 830 rpm for manual transmissions (in Neutral), or 630 rpm for automatic transmissions (in Drive).
  4.  
  5. Adjust both mixture screw equally inward to obtain 750 rpm for manual transmissions or 600 rpm for automatics (in Drive).
  6.  
  7. Disconnect the solenoid wire, set the carburetor idle screw to obtain 450 rpm, and reconnect the solenoid.
  8.  
  9. Reconnect the distributor vacuum line.
  10.  

V8-350 (300 HP) & 402 (330 HP) ENGINES
  1. Turn in both mixture screws until they gently seat, then back them out four turns.
  2.  
  3. Adjust the carburetor idle screw to obtain 775 rpm for manual transmission, 630 rpm for automatics (in Drive).
  4.  
  5. Adjust the mixture screw equally to obtain 700 rpm for manual transmission, 600 rpm for automatics (in Drive).
  6.  
  7. Reconnect the distributor vacuum line.
  8.  

V8-402 (350 HP) & 454 ENGINES
  1. Turn in both mixture screws until they gently seat, then back them out four turns.
  2.  
  3. Adjust the carburetor idle screw to obtain 700 rpm for manual transmission or 630 rpm for automatics (in Drive).
  4.  
  5. For cars with automatic transmission: adjust the mixture screws equally to obtain 600 rpm with the transmission in Drive.
  6.  
  7. For cars with manual transmissions: Turn in one mixture screw until the speed drops to 400 rpm, then adjust the carburetor idle screw to obtain 700 rpm. Turn in the other mixture screw until the speed drops 400 rpm, then regain 700 rpm by adjusting the carburetor idle screw.
  8.  
  9. Reconnect the distributor vacuum line.
  10.  

1971-72 Initial Adjustments

Adjust with air cleaner installed. The following initial idle adjustments are part of the normal engine tune-up. There should be a tune-up decal placed conspicuously in the engine compartment outlining the specific procedure and settings for each engine application. Follow all of the instructions when adjusting the idle. These tuning procedures are necessary to obtain the delicate balance of variables for the maintenance of both reliable engine performance and efficient exhaust emission control.

All engines have limiter caps on the mixture adjusting screws. The idle mixture is preset and the limiter caps installed at the factory in order to meet emission control standards. Do not remove these limiter caps unless all other possible causes of poor idle condition have been thoroughly checked out. The solenoid used on 1971 carburetors is different from the one used on earlier models. The Combination Emission Control System (C.E.C.) solenoid valve regulates distributor vacuum as a function of transmission gear position.The C.E.C solenoid is adjusted only after: 1) replacement of the solenoid, 2) major carburetor overhaul, or 3) after the throttle body is removed or replaced.

All initial adjustments described below are made:

  1. With the engine warmed up and running.
  2.  
  3. With the choke fully open.
  4.  
  5. With the fuel tank line disconnected from the Evaporative Emission canister on all models.
  6.  
  7. With the vacuum hose disconnected at the distributor and plugged.
  8.  

Be sure to reconnect the distributor vacuum hose and to connect the fuel tank-to-evaporative emission canister line or install the gas cap when idle adjustments are complete.

6-CYLINDER 250 ENGINE
  1. Adjust the carburetor idle speed screw to obtain 550 rpm (700 rpm of 1972) for manual transmissions (in Neutral) or 550 rpm (600 rpm for 1972) for automatics (in Drive). Do not adjust the solenoid screw. Using the solenoid screw to set idle or incorrectly adjusting it may result in a decrease in engine braking.
  2.  
  3. Reconnect the vapor line and distributor vacuum advance line.
  4.  

V8-307 & 350 (2-BBL) ENGINES
  1. On 1971 models, adjust the carburetor idle speed screw to obtain 600 rpm for manual transmission (in Neutral) with the air conditioning turned off, or 550 rpm for automatic transmissions (in Drive) with the air conditioning turned on. Do not adjust the solenoid screw. On 1972 models, turn the air conditioning off and adjust the idle stop solenoid screw to obtain 900 rpm for manual transmissions (in Neutral) or 600 rpm for automatics (in Drive). Place the transmission in Park or Neutral and adjust the fast idle cam screw to get 1,850 rpm on 307 engines and 2,200 rpm on 350 engines.
  2.  
  3. Reconnect the vapor line and distributor vacuum advance line.
  4.  

V8-350 (4-BBL) ENGINE
  1. On 1971 models, adjust the carburetor idle speed screw to obtain 600 rpm for manual transmissions (in Neutral) with the air conditioning turned off, or 550 rpm for automatics (in Drive) with the air conditioning turned on. Do not adjust the solenoid screw. On 1972 models, turn the air conditioning off and adjust the idle stop solenoid screw to get 800 rpm for manual transmissions (in Neutral) or 600 rpm for automatic transmissions (in Drive).
  2.  
  3. For both 1971 and 1972 models, place the fast idle cam follower on the second step of the fast idle cam, turn the air conditioning off and adjust the fast idle to 1,350 rpm for manual transmissions (in Neutral) or 1,500 rpm for automatics (in Park).
  4.  
  5. Reconnect the vapor line and the distributor vacuum advance line on all models.
  6.  

V8-402 & 454 ENGINES
  1. On 1971 models, turn off the air conditioner and adjust the carburetor idle speed screw to obtain 600 rpm with manual transmissions in Neutral and automatics in Drive. Do not adjust the solenoid screw. On 1972 cars, turn off the air conditioning and adjust the idle stop solenoid screw to 800 rpm (in Neutral) for manual transmissions and 600 rpm (in Drive) for automatics.
  2.  
  3. On both 1971 and 1972 cars, place the fast idle cam follower on the second stop of the fast idle cam, turn off the air conditioner and adjust the fast idle to 1,350 rpm for manual transmissions (in Neutral) or 1,500 rpm for automatics (in Park).
  4.  
  5. Reconnect the vapor line and the distributor vacuum line on 1971 and 1972 cars.
  6.  

1973
INITIAL ADJUSTMENTS

All models are equipped with idle limiter caps and idle solenoids. Disconnect the fuel tank line from the evaporative canister. The engine must be running at operating temperature, choke off, parking brake on, and rear wheels blocked. Disconnect the distributor vacuum hose and plug it. After adjustment, reconnect the vacuum and evaporative hoses.

6-CYLINDER 250 ENGINE

Adjust the idle stop solenoid for 700 rpm on manual transmission models or 600 rpm on automatics (in Drive). On manual models, make no attempt to adjust the CEC solenoid (the larger of the two carburetor solenoids) or a decrease in engine braking could result.

V8-307, 350 & 400 (2-BBL) ENGINES
  1. With the air conditioning Off, adjust the idle stop solenoid screw for a speed of 900 rpm on manual models; 600 rpm for automatics in Drive.
  2.  
  3. Disconnect the idle stop solenoid electrical connector and adjust the idle speed screw (screw resting on lower stop of the cam) for 450 rpm on all 307 cu. in. engines, 400 rpm on 350 and 400 engines with automatic transmissions, or 500 rpm or 350 and 400 cu. in engine with manual transmissions.
  4.  

V8-350 & 400 (4-BBL) ENGINES
  1. Adjust the idle stop solenoid screw to 900 rpm (manual), 600 rpm (automatic in Drive).
  2.  
  3. Connect the distributor vacuum hose and position the fast idle cam follower on the top step of the fast idle cam (turn air conditioning off) and adjust the fast idle to 1,300 rpm on manual transmission 350 engines; 1,600 rpm for all automatics in Park.
  4.  

V8-454 ENGINE
  1. With the air conditioning off, adjust the idle stop solenoid screw to 900 rpm for the manual transmission; 700 rpm with the automatic transmission in Drive.
  2.  
  3. Connect the distributor vacuum hose and place fast idle cam follower on the top step of the fast idle cam. Adjust the fast idle to 1,300 rpm for manual transmission; and 1,600 rpm for automatic transmissions (in Park).
  4.  



Click image to see an enlarged view

Fig. Fig. 1: Disconnect EVAP canister vapor line from carburetor to prevent canister purge from enrichening mixture during adjustment



Click image to see an enlarged view

Fig. Fig. 2: If equipped with an EGR valve, most adjustments require that the line be disconnected and plugged as well

1974
INITIAL ADJUSTMENTS

All models are equipped with idle limiter caps and idle solenoids. Disconnect the fuel tank line from the evaporative canister. The engine must be running at operating temperature, choke off, parking brake on, and rear wheels blocked. Disconnect the distributor vacuum hose and plug it. After adjustment, reconnect the vacuum and evaporative hoses.

6-CYLINDER 250 ENGINE

Using the hex nut on the end of the solenoid body, turn the entire solenoid to get 850 rpm for the manual transmission, 600 rpm for automatic transmissions in Drive.

V8-350 & 400 (2-BBL) ENGINES
  1. Turn the air conditioning off. Adjust the idle stop solenoid screw for 900 rpm on manual; 600 rpm on automatic (in Drive).
  2.  
  3. De-energize the solenoid and adjust the carburetor idle cam screw (on low step of cam) for 400 rpm on automatic models (in Drive); 500 rpm on 350 engines with manual transmission.
  4.  

V8-350 & 400 (4-BBL) ENGINES
  1. Turn the air conditioning off. Adjust the idle stop solenoid screw for 900 rpm on manual transmission models; 600 rpm on automatic (in Drive).
  2.  
  3. Connect the distributor vacuum hose. Position the fast idle cam follower on the top step of the fast idle cam and adjust the fast idle speed to 1,300 rpm on manual; 1,600 on automatic (in Park).
  4.  

V8-454 ENGINE
  1. With the air conditioning off, adjust the idle stop solenoid screw for 800 rpm with the manual transmission; 600 with the automatic transmission in Drive.
  2.  
  3. Reconnect the distributor vacuum advance hose and place the fast idle cam follower on the top step of the fast idle cam. With the air conditioning off, adjust the fast idle to 1,600 rpm for manual transmissions; 1,500 rpm for all automatics in Park.
  4.  



Click image to see an enlarged view

Fig. Fig. 3: On most carburetors, adjust the slow idle speed using throttle stop screw



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Fig. Fig. 4: On carburetors so equipped, adjust the idle-up solenoid using a wrench



Click image to see an enlarged view

Fig. Fig. 5: On most carburetors, adjust the fast idle speed using the choke adjustment screw

1975-76

See Figure 6

6-CYLINDER 250 (1-BBL) ENGINE
  1. Idle speed is adjusted with the engine at normal operating temperature, air cleaner on, choke open, and air conditioning off (air models). Hook up a tachometer to the engine.
  2.  
  3. Block the rear wheels and apply the parking brake.
  4.  
  5. Disconnect the fuel tank hose from the evaporative canister.
  6.  
  7. Disconnect and plug the distributor vacuum advance hose.
  8.  
  9. Start the engine and check the ignition timing. Adjust if necessary.
  10.  

Reconnect the vacuum hose. To adjust the idle speed, turn the solenoid in or out to obtain the higher of the two specifications listed on the decal. With the automatic transmission in Drive or the manual transmission in Neutral, disconnect the solenoid electrical connector and turn the 1 / 8 in. Allen screw in the end of the solenoid body to the lower idle speed.

  1. Place the shift lever in Drive on cars with automatic transmissions and have an assistant apply the brakes. On cars with manual transmissions, put it into Neutral.
  2.  
  3. Cut the tab off the mixture limiter cap, but don't remove the cap. Turn the screw counterclockwise until the highest idle speed is reached.
  4.  
  5. Set the idle speed to the higher of the two listed idle speed by turning the solenoid in or out.
  6.  
  7. Check the tachometer and turn the mixture screw clockwise until the idle speed is at the lower of the two listed idle speeds.
  8.  
  9. Shut off the engine, remove the tachometer, and reconnect the carbon canister hose.
  10.  



Click image to see an enlarged view

Fig. Fig. 6: Idle speed adjustment on a common carburetor for the 1976-78 6-cylinder engines

V8-350 (2-BBL) ENGINE
  1. Idle speed is adjusted with the engine at normal operating temperature, air cleaner on, choke open, and air conditioning off. Hook up a tachometer to the engine.
  2.  
  3. Block the rear wheels and apply the parking brake.
  4.  
  5. Disconnect the fuel tank hose from the evaporative canister.
  6.  
  7. Disconnect and plug the distributor vacuum advance hose.
  8.  
  9. Start the engine and check the ignition timing. Adjust if necessary, then reconnect the vacuum hose.
  10.  
  11. Adjust the idle speed screw to the specified rpm. If the figures given in the Tune-Up Specifications chart differ from those on the tune-up decal, those on the decal take precedence. Automatic transmissions should be in Drive, manual transmissions should be in Neutral.
  12.  


CAUTION
Make doubly sure that the rear wheels are blocked and that the parking brake is applied.

  1. Adjust the idle speed to the higher of the two figures on the tune-up decal. Back out the two mixture screws equally until the highest idle is reached. Reset the speed if necessary to the higher one on the tune-up decal. Next, turn the screws in equally until the lower of the two figures on the decal is obtained.
  2.  
  3. Shut off the engine, reconnect hose to evaporative canister, and remove blocks from wheels.
  4.  

V8-350, 400 & 454 ENGINES

1975 4-barrel carburetors are equipped with idle stop solenoids. There are two idle speeds, one with the solenoid energized and second with the solenoid de-energized. Both are set using the solenoid. The slower speed (solenoid de-energized) is necessary to prevent dieseling by allowing the throttle plate to close further than at a normal idle speed.

  1. Idle speed is set with the engine at normal operating temperature, air cleaner on, choke open, and air conditioning off. Hook up a tachometer to the engine.
  2.  
  3. Block the rear wheels and apply the parking brake.
  4.  
  5. Disconnect the fuel tank hose from the evaporative canister.
  6.  
  7. Disconnect and plug the distributor vacuum advance hose.
  8.  
  9. Start the engine and check the ignition timing. Adjust if necessary, then reconnect the vacuum hose.
  10.  

For 1976, the idle solenoid has been dropped. To adjust the idle, follow Steps 1-5, skip Steps 6, 7, and 8, then follow Steps 9 and 10, using the idle speed screw.

  1. Disengage the electrical connector at the idle solenoid.
  2.  
  3. Set the transmission in Drive, then adjust the low idle speed screw for the lower of the two figures given for idle speed.
  4.  


CAUTION
Make sure that the drive wheels are blocked and the parking brake is applied.

  1. Reconnect the idle solenoid and open the throttle slightly to extend the solenoid plunger.
  2.  
  3. Turn the solenoid plunger screw in or out to obtain the higher of the two idle speed figures (this is normal curb-idle)
  4.  
  5. To adjust the mixture, break off the limiter caps. Make sure that the idle is at the higher of the two speeds listed on the decal. Turn the mixture screws out equally to obtain the highest idle. Reset the idle speed with the plunger screw if necessary. Turn the mixture screw in until the lower of the two figures on the decal is obtained.
  6.  
  7. Shut off the engine, remove blocks from drive wheels, and reconnect hose to evaporative canister.
  8.  

1977

See Figures 7 and 8

  1. First satisfy all the following requirements:
    1. Set parking brake and block drive wheels.
    2.  
    3. Bring the engine to operating temperature.
    4.  
    5. Remove the air cleaner for access, but make sure all hoses stay connected.
    6.  
    7. Consult the Emission Control Information label under the hood, and disconnect and plug hoses as required by the instructions there.
    8.  
    9. Connect an accurate tach to the engine.
    10.  

  2.  
  3. Set ignition timing as described above.
  4.  
  5. Remove the cap(s) from the idle mixture screw(s). Remove caps carefully, to prevent bending these screws.
  6.  
  7. Turn in the screw(s) till they seat very lightly, then back screw(s) out just far enough to permit the engine to run.
  8.  
  9. Put automatic transmission in Drive.
  10.  



Click image to see an enlarged view

Fig. Fig. 7: Idle speed adjustment on a 4BBL, V8 engine with solenoid-1977



Click image to see an enlarged view

Fig. Fig. 8: Idle speed adjustment on a 4BBL, V8 engine without solenoid-1977

  1. Back out screw(s) 1 / 8 turn at a time, going alternately from screw to screw after each 1 / 8 turn where there are two screws, until the highest possible idle speed is achieved. Then, set the idle speed as follows: 250 CID engine with manual transmission - 950; with automatic - 575; with automatic in California - 640; with automatic used in higher altitude area - 650; 305 V8 with manual transmission - 650; with automatic - 550; standard 350 V8 with automatic - 550; 350 V8 used at high altitudes - 650.
  2.  
  3. After setting the idle speed, repeat the mixture adjustment to ensure that mixture is at the point where highest idle speed is obtained. Then, if idle speed has increased, repeat idle speed adjustment of Step 6.
  4.  
  5. Now, turn screw(s) in, going evenly in 1 / 8 turn increments where there are two, until the following idle speed are obtained: 250 CID engine with manual transmission - 750; with automatic - 550; with automatic in California - 600; with automatic used in high altitude areas - 600; 305 V8 with manual transmission - 600; with automatic - 500; standard 350 V8, manual transmission - 700; standard 350 V8 with automatic - 500; 350 V8 used at high altitudes - 600.
  6.  
  7. Reset idle speed to the value shown on the engine compartment sticker, if that differs from the final setting in the step above.
  8.  
  9. Check and adjust fast idle as described on the engine compartment sticker. See Fuel System .
  10.  
  11. Reconnect any vacuum hoses that were disconnect for the procedure, and install the air cleaner.
  12.  
  13. If idle speed has changed, reset according to the engine compartment sticker. Disconnect tach.
  14.  

1978-80

See Figures 9, 10, 11, 12, 13 and 14

These models have sealed idle mixture screws; in most cases these are concealed under staked-in plugs. Idle mixture is adjustable only during carburetor overhaul, and requires the addition of propane as an artificial mixture enrichener.

See the emission control label in the engine compartment for procedures and specifications not supplied here. Prepare the car for adjustment (engine warm, choke open, fast idle screw off the fast idle cam) as per the label instructions.

1-BBL
  1. Run the engine to normal operating temperature.
  2.  
  3. Make sure that the choke is fully opened.
  4.  
  5. Turn the A/C off and disconnect the vacuum line at the vapor canister. Plug the line.
  6.  
  7. Set the parking brake, block the drive wheels and place the transmission in Drive (AT) or Neutral (MT). Connect a tachometer to the engine according to the manufacturer's instructions.
  8.  
  9. Turn the solenoid assembly to achieve the solenoid-on speed.
  10.  
  11. Disconnect the solenoid wire and turn the 1 / 8 in. hex screw in the solenoid end, to achieve the solenoid-off speed.
  12.  
  13. Remove the tachometer, connect the canister vacuum line and shut off the engine.
  14.  

2-BBL AND 4-BBL (EXCEPT V8-350 ENGINE)
  1. Run the engine to normal operating temperature.
  2.  
  3. Make sure that the choke is fully opened, turn the A/C off, set the parking brake, block the drive wheels and connect a tachometer to the engine according to the manufacturer's instructions.
  4.  



Click image to see an enlarged view

Fig. Fig. 9: Idle speed adjustment on a 2BBL, with solenoid-1978-79



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Fig. Fig. 10: Idle speed adjustment on a 2BBL, without solenoid-1978-79

  1. Disconnect and plug the vacuum hoses at the EGR valve and the vapor canister.
  2.  
  3. If equipped with an automatic transmission, place the transmission in Park. If equipped with a manual transmission, place transmission in Neutral.
  4.  
  5. Disconnect and plug the vacuum advance hose at the distributor. Check and adjust the timing.
  6.  
  7. Connect the distributor vacuum line.
  8.  



Click image to see an enlarged view

Fig. Fig. 11: Idle speed adjustment on a 4BBL, without solenoid-1979 and later vehicles



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Fig. Fig. 12: Idle speed adjustment on a 4BBL, with solenoid-1979 and later vehicles

  1. Manual transmission cars without A/C and without solenoid: place the idle speed screw on the low step of the fast idle cam and turn the screw to achieve the specified idle speed.
  2.  
  3. If equipped with A/C: set the idle speed screw to the specified rpm. Disconnect the compressor clutch wire and turn the A/C on. Open the throttle momentarily to extend the solenoid plunger. Turn the solenoid screw to obtain the specified rpm. Finally, adjust the fast idle speed using the choke screw on the opposite side of the carburetor assembly.
  4.  



Click image to see an enlarged view

Fig. Fig. 13: Idle speed adjustment on a 2BBL, with solenoid-1980



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Fig. Fig. 14: Idle speed adjustment on a 2BBL, without solenoid-1980

  1. Automatic transmission cars without A/C: manual transmission cars without A/C, solenoid-equipped carburetor: momentarily open the throttle to extend the solenoid plunger. Turn the solenoid screw to obtain the specified rpm. Disconnect the solenoid wire and turn the idle speed screw to obtain the slow engine idle speed.
  2.  

V8-350 ENGINE
  1. Run the engine to normal operating temperature.
  2.  
  3. Set the parking brake and block the drive wheels.
  4.  
  5. Connect a tachometer to the engine according to the manufacturer's instructions.
  6.  
  7. Disconnect and plug the purge hose at the vapor canister, then disconnect and plug the EGR vacuum hose at the EGR valve.
  8.  
  9. Turn the A/C off.
  10.  
  11. Place the transmission in Park (Automatic) or Neutral (Manual).
  12.  
  13. Disconnect and plug the vacuum advance line at the distributor. Check and adjust the timing.
  14.  
  15. Connect the vacuum advance line. Place the automatic transmission in Drive.
  16.  
  17. Manual transmission cars without A/C: adjust the idle stop screw to obtain the specified rpm. If equipped with A/C: with the A/C Off, adjust the idle stop screw to obtain the specified rpm. Disconnect the compressor clutch wire and turn the A/C On. Open the throttle slightly to allow the solenoid plunger to extend. Turn the solenoid screw to obtain the solenoid rpm listed on the underhood emission sticker.
  18.  
  19. Connect all hoses and remove the tachometer.
  20.  

1981-82

See Figure 15

Most of the E2ME (two barrel) and E4ME (four barrel) carburetors used on these models are equipped with an Idle Speed Control (ISC) assembly, monitored by the ECM, which controls which controls engine idle speed. The curb idle is programmed into the ECM and is not adjustable. Some models with A/C may be equipped with an Idle Speed Solenoid (ISS), if so, refer to the 1978-80 procedure.



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Fig. Fig. 15: Common Idle Speed Control (ISC) assembly

1983-88

See Figures 15 and 16

The E2ME (two barrel) and the E4ME (four barrel) carburetors used on these models all are equipped with an Idle Speed Control (ISC) assembly, monitored by the ECM, which controls engine idle speed. The curb idle is programmed into the ECM and is not adjustable.



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Fig. Fig. 16: Common Idle Load Compensator (ILC)

On the E4MC models, an Idle Load Compensator (ILC) mounted on the float bowl is used to control curb idle speeds. No attempt should be made to adjust this since it is controlled by the ECM.

On vehicles that do not include an ISC or ILC but are equipped with air conditioning, an Idle Speed Solenoid (ISS) is used to maintain curb idle speed any time the air conditioner compressor clutch is engaged. If so refer to the 1978-80 procedures.

 
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