Volkswagen Air-Cooled 1970-1981 Repair Guide

Deceleration Control

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All 1975 and later Type 1 and Type 2 manual transaxle models, Type 2 automatic transaxle models after chassis No. 226 2 077 583, and Type 3 and 4 California manual transaxle models are equipped with vacuum operated deceleration valves. The deceleration valve prevents an overly rich mixture from reaching the exhaust. During deceleration, the valve opens, allowing air to bypass the throttle plate and enter the combustion chamber, thereby leaning the air/fuel mixture. Type 2 automatic transaxle models up to chassis No. 226 2 077 583 and Type 3 and 4 California automatic transaxle models have electrically operated deceleration valves which are activated by the transaxle.

CHECKING THE DECELERATION VALVE



Vacuum Type

See Figure 1

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Fig. Fig. 1: Identification of the components and vacuum lines used on the vacuum operated deceleration valve system

The deceleration valve on the Type 1 is located on the engine compartment hood left hinge mount. It is at the center front of the engine between the fuel injection intake air sensor on the Type 2 (don't confuse it with the EGR canister).

A faulty deceleration valve will cause engine speed to be higher than normal at idle. To test the valve, pinch shut the large fabric covered hose leading into the air cleaner. If the idle speed drops, the valve is faulty and should be replaced.

Electrical Type See Figure 2

Click image to see an enlarged view

Fig. Fig. 2: The electrically operated deceleration valve is attached to only 2 vacuum lines-as compared to 3 on the vacuum operated valve

  1. From under the vehicle, remove the wire from the automatic transaxle fluid pressure switch which runs to the deceleration valve. The valve is located on the intake air distributor.
  2.  
  3. Turn the ignition ON, and ground the disconnected wire against the transmission housing or the chassis frame.
  4.  
  5. An audible click should be heard. If not, replace the deceleration valve or the automatic transaxle fluid pressure switch.
  6.  

 
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