Poor idle

[302Z28]

Car is '92 Metro with manual trans. Idle has been set to factory spec (850) RPM. Engine idles smooth until electrical load is applied i.e. lights, wipers, heater. Engine then slows and starts rocking. Cooling fan almost kills engine!
Shouldn't the computer keep the idle at 850 RPM?
Thanks,
Ray

[megawayne]

mine does this too. If you find anything out please let me know. I will do the same. I am going to get a friend to help me located the idle up sensor? I never heard of it, but he says when something pulls a load it idles the car up to compensate. My air conditioning does the same.

[mickkey3rd]

Hi

A possible solution is to check the ISC valve (Idle Speed Control) it is a black cylinder about an inch in diameter with two vacuum hoses going to it. It is located behind and just under the Throttle Body.
The ECM when a load is sensed, by the diode module, will pulse this valve to allow more air pass the throttle plate. This is how the ECM controls idle speed. Check the coil on the ISC to make sure is is not open. Also check hoses etc for clogs.
A quick check of the Positive Crankcase Ventilation valve may also be in order. If it is allowing blowby into the intake at idle this will cause problems also.

Joe

Originally Posted by 302Z28

Car is '92 Metro with manual trans. Idle has been set to factory spec (850) RPM. Engine idles smooth until electrical load is applied i.e. lights, wipers, heater. Engine then slows and starts rocking. Cooling fan almost kills engine!
Shouldn't the computer keep the idle at 850 RPM?
Thanks,
Ray