We have a cavalier 2.0 16v ecotec of the 1995 vintage which is currently giving me some grief. It was fine until I replaced the faulty thermostat (gauge only reached top of blue). The guage now reaches the 90 degree mark but since then there has been a problem with the idling. It has done 130,000 miles.
I can be sitting at traffic lights or junction with the correct idle speed, but after a while the idle speed reduces until the engine nearly stalls. Sometimes it will recover and resume normal idling, but very frequently it stalls. After restarting, there is some hesitation at low revs/part throttle for a short time.
Thus far I have done the following in my attempts to cure the fault:
- Remove, dismantle and clean the idle speed control valve. Internal moving parts now operating freely.
- Cleaned the throttle body and butterfly with carb cleaner and stiff brush - now spotless.
- Cleared blocked crankcase breather pipes and stub on manifold. Vacuum now present on small hose connected to cam cover.
- Cleaned air-mass meter with brake cleaner (was replaced less than 2 years ago).
After searching this group on google, I found an old article where someone suggested adjusting the throttle stop screw to give an idle speed of 500rpm with the ISCV unplugged and a hot engine, thus preventing stalling. I tried this but the idling is too unstable. I can set it to 500rpm, but after a short time it will either stall or rev-up slightly, even with the ISCV unplugged! Why?
Before I unplugged the ISCV there was no fault codes stored in the ECU. All routine servicing has regularly been performed in the 18 months we have owned it including oil, oil filter, spark plugs (GM) and air filter. It runs perfectly except for this intermittent idling fault, and recent emmissions test (before I changed the thermostat) results were: Fast idle: 2768 rpm, CO 0.00%, HC 6ppm, Lambda 1.015 Natural idle: 927rpm, CO 0.00%
Despite all my efforts, the fault persists. As I have discussed, the ECU and emissions test suggest no faults and ISCV *appears* to work properly. Any ideas?
Thanks guys (and gals?) James of Sunderland