I appeal to the mechanically inclined of the teeming millions. I already posted my question on the car talk site, but I wanted to see if any dopers might be able to help. Here goes:
I have a 1990 Chevy Lumina van (Ugly Van TM) with the V6. When cold it runs fine. Once warm it chokes from idle (1500, too high?) to 2000 RPM. Once past 2000 it runs fine. It will stall at stoplights while accelerating (bad thing). It warms up very quickly and is running hot. I took it to a mechanic and he put it on the computer. He found no error codes, but the TPS was running 4 volts instead of 5. He switched it and there was no change so he switched it back. Then he said the distributor advance was malfunctioning. Replaced the distributor. He said it was better but not fixed. He checked the injectors and said one was not right. He rebuilt it. I needed the car so I took it back and it is still not right. Any input would be appreciated. Thanks,
John
P.S. When I first took it to the mechanic it was choking cold or hot, so I guess it is a little better. Also, I did not notice if it was running hot before I took it to the mechanic.
Sounds like a fuel delivery issue, so the injector lead was a decent one. Doesn’t sound electrical in nature.
I would suspect that the fuel/air ratio which is controlled by the computer is screwed up because of a temp sensor…or…your car is running hot because of a bad thermostat (closed…partly closed) which would lead to the car warming up real fast and possibly running to hot at idle and low rpm.
You may have poor performing injectors, and the rebuild on the very bad one was enough to fix some of the problems.
Might also be a vacuum leak in the intake manifold that only opens up when the engine is warm.
I’ve been told that this can be checked by venting a small amount of propane around suspicious portion of intake manifold while engine is running – engine will speed up if there is a leak. I’ve never done this myself and it sounds dangerous. Can a mechanic comment on this technique?
Philster, thanks for the input. I forgot to mention that the mechanic did check the fuel pump and found the pressure to be in the normal range, so gas is getting to the throttle body. Is it possible the MAP sensor is bad but not sending the error code to the computer?
Rufus, I have considered a vacuum leak. I hope it is something easier to find. Rather than using propane I would use starting fluid (ether) to hunt for the leak.
I will try edmunds. I did run two cans of STP injector cleaner through it when it started running rough. Also, the mechanic did check the injectors and rebuilt one of the two. Thanks for the tips.