Toyota Celica 1986-1993 Repair Guide

Idle Speed Control

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The ECU is programmed with specific engine speed values to respond to different engine conditions (coolant temperature, air conditioner on/off, etc.). Sensors transmit signals to the ECU which controls the flow of air through the by-pass of the throttle valve and adjusts the idle speed to the specified value. Some vehicles use an Idle Speed Control (ISC) valve while others use an Air Valve to control throttle body by-pass air flow.

TESTING



Air Valve


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Fig. Fig. 1 Pinching air valve hose2S-E engine



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Fig. Fig. 2 Checking air valve heat coil resistance2S-E engine



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Fig. Fig. 3 Pinching air valve hose3S-GE engine

2S-E ENGINE
  1. With the engine running and the coolant temperature below 140°F (60°C), pinch off the air valve hose and verify that the idle rpm drop. With a warm engine, check that the rpm are reduced by no more than a 100 rpm.
  2.  
  3. Disconnect the valve wire connector and measure the heat coil resistance with the valve warm. It should be 40-60 ohms between terminals Fp and E1 with the coolant temperature at 176°F (80°C) and the air valve closed.
  4.  
  5. If not as specified, replace the valve.
  6.  

3S-GE ENGINE
  1. With the engine running and the coolant temperature below 140°F (60°C), turn the idle speed adjusting screw in. The idle rpm should drop.
  2.  
  3. With a warm engine, pinch the air valve hose and check that the rpm are reduced by no more than a 100 rpm.
  4.  
  5. If not as specified, service or replace the air valve.
  6.  

Idle Speed Control (ISC) Valve


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Fig. Fig. 4 Checking ISC valve resistance3S-FE engine



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Fig. Fig. 5 Checking ISC valve resistance5S-FE engine



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Fig. Fig. 6 Disconnecting ISC valve1988-89 3S-GTE engine



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Fig. Fig. 7 Disconnecting ISC valve1990-93 3S-GTE engine

3S-FE AND 5S-FE ENGINES

WARNING
The idle speed must be set correctly before testing the ISC valve.

  1. Bring the engine to normal operating temperature with transmission in N .
  2.  
  3. Using a jumper wire, connect the terminals T or te1 and E1 of the check connector.
  4.  
  5. The engine rpm should rise to 1,000-1,300 rpm for 5 seconds. If rpm is as specified, the valve is functioning properly.
  6.  
  7. If rpm did not function as specified, stop the engine and disconnect the jumper wire.
  8.  
  9. Disconnect the ISC valve connector.
  10.  
  11. Using an ohmmeter, measure the resistance between the +B terminal (middle terminal) and the ISC1 (ISCC) and ISC2 (ISCO) outer terminals.
  12.  
  13. The resistance should be 16-17 ohms on the 3S-fe engine or 19.3-22.3 ohms on the 5S-fe engine.
  14.  
  15. If not as specified, replace the ISC valve.
  16.  

3S-GTE ENGINE

WARNING
The idle speed must be set correctly before testing the ISC valve.

  1. Bring the engine to normal operating temperature with transmission in N .
  2.  
  3. Disconnect the ISC valve connector.
  4.  
  5. The engine rpm should rise to 1,000 or more.
  6.  
  7. Reconnect the connector and check that the rpm return to idle speed. If not, check the valve, wiring and ECU.
  8.  
  9. With the engine off, disconnect the ISC valve connector.
  10.  
  11. Using an ohmmeter, measure the resistance on 1988-89 models between the +B terminal (middle terminal) and the other terminals. The resistance should be 16-17 ohms.
  12.  
  13. Using an ohmmeter, measure the resistance on 1990-93 models between the +B terminal (middle terminal) and the other terminals. The resistance should be 19.3-22.3 ohms.
  14.  
  15. If not as specified, replace the ISC valve.
  16.  

Auxiliary Air Valve


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Fig. Fig. 8 Closing the auxiliary air valve port4A-FE engine

4A-FE ENGINE
  1. Disconnect the air cleaner hose from the throttle body.
  2.  
  3. Check the valve operation:
    1. Check the engine rpm by closing the air valve port on the throttle body.
    2.  
    3. At low temperature, below 176 degrees F, when the air valve port is closed the engine rpm should drop.
    4.  
    5. After warm up when the air valve is closed, the rpm should not drop more than 50 rpm.
    6.  

  4.  
  5. If operation is not as specified, replace the valve.
  6.  

 
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