Volkswagen Golf/Jetta 2 manual

Idle speed boost (air conditioned models) - testing and idle speed adjustment
Fuel and exhaust systems - K-Jetronic fuel injection - 8 valve engines / Idle speed boost (air conditioned models) - testing and idle speed adjustment

1 The function of this device is to stabilise the engine speed when it drops below 700 rpm under certain operating conditions. This is achieved by increasing the air supply to the engine, which raises the idling speed to approximately 1050 rpm. At this point, the air supply valve is cut off and the idle speed then returns to normal. The two valves which control this system are attached to the right-hand front suspension mounting in the engine compartment (see illustration).

6.1 Idle speed boost valve check
6.1 Idle speed boost valve check

1 Valve No 1
2 Valve No 2
3 Hose

2 Valve No. 1 (inboard side) increases the engine speed when it drops below 700 rpm, whilst valve No. 2 (outboard side) increases the idle speed when the air conditioner is switched on.

Valve 1 - testing and idle speed adjustment
3 Run the engine up to its normal operating temperature, switch off the air conditioner and allow the engine to idle. With the exception of the air conditioner, switch on all electrical consumers (lights, etc.), then adjust the idle speed to 700 rpm. When reaching idle speed, the valve should open and the idle speed increase. Using a pair of pliers, pinch the air hose from the valve then check that the speed drops.

4 Switch off all electrical consumers, then pinch the air hose again and adjust idle speed to that specified. When the correct idle speed is reached, unclamp the hose. The idle speed should then increase up to about 1050 rpm at which point the valve will close and the speed drop to the specified idle speed setting.

Valve 2 - checking
5 Run the engine at normal idle speed with the air conditioner switched off. Pinch the air hose and check that the engine speed remains the same.

6 Now switch the air conditioning on and repeat the test. When the hose is pinched, the engine speed should drop.

7 If the air hose and/or valves Nos. 1 or 2 are disconnected or removed for any reason, it is important when refitting to note that the three-way hose connector large hole must go to valve No. 2.

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