Most of the time, the vehicle idles smoothly at stop signs and red lights. Occasionally, the car will idle very roughly when I come to a stop – often stalling. Even if I drop it into Neutral, it will shake and stall. This problem can last for a few minutes and up to a few hours. To get it moving again, I drop it into Neutral, give it about 25% throttle, start it, rev it up to 2500 and quickly drop it into drive. Once moving, it accelerates and cruises smoothly.
The car always starts and warms up without idle issues. The problem only occurs when the engine reaches normal operating temperature.
Coincidence? Maybe. But immediately after filling up the tank, it started idling roughly. Since then, I have re-filled the tank at least 4 times, pouring in a bottle of HEET each time, but the issue still persists.
NOTE: put a new exhaust system on the car 2 years ago. The check engine light stays on, complaining about both non-OEM O2 sensors. The car has run smoothly for 2 years despite the codes.
NOTE: Aside from the O2 sensor codes above, no other codes are stored to help troubleshoot this intermittent rough idle issue.
Observation: when it starts idling roughly, if I drop it into Neutral and rev the RPM’s to 5000 and hold for a couple seconds, about 80% of the time, it will drop back to idle and run smoothly until the light turns green.
While idling roughly in Park, if I rev the engine to 2500 RPM and slowly drop the RPM’s with the throttle, the engine starts to idle roughly at about 1400 RPM and gets progressively worse as I slowly back off the throttle. By the time I reach 750 RPM, it is idling so rough the RPM’s bounce up and down until it stalls.
So far, I have used several bottles of HEET, cleaned the throttle body and fuel injectors. Is there an easy way to tell if I have a lot water in the gas tank?
I have read other posts in this forum with the following suggestions:
– vacuum leak
– moisture in electrical clips/wiring harnesses
– clean the contacts on throttle position sensor
– bad pin(s) in sensor clip
Additional suggestions are welcome. Thanks!
