Questions and Answers
Chevrolet Cavalier Z-24 Won't Idle Right
Q. Hello. I recently have purchased a 1986 Z-24 Chevrolet Cavalier. It has an automatic transmission, no ABS. The mileage is roughly 130,000. It has a 2.8 engine and is fuel injected.
Anyways, the problem is that when the engine is cold and I start it, the idle is very rough. It will speed up and then slow down to the point that it almost (and sometimes does) stall out. But, after it gets warm, that goes away and it evens out.
When I make a complete stop, it stumbles and then after about a second picks up. I have already replaced the O2 sensor, the throttle position sensor has been tested and that is okay and I have also replaced the EGR valve. Nothing has changed.
My trouble codes were reading O2 sensor and EGR valve; both a mechanic and myself tested this. I used the trouble code keys and he used the diagnostic machine. Please help.
A. There are two suggestions I can make here, one is to give the throttle a good cleaning and the other is related to a TSB that GM issued on this car.
Carbon gums build up at that small opening between the throttle bore and the throttle plate. This tends to throw off the air/fuel mixture. Your computer sets the mixture assuming a certain amount of air to be passing the throttle plate. When carbon blocks the air the mixture becomes skewed until the O2 sensor kicks in to make the adjustments.
The TSB refers to replacing the ECU's PROM to correct an inherently lean mixture.
Additional Information provided courtesy of ALLDATA
