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CTD20 · 04-16-2006, 11:32 PM

My 91 NA does something similar. After it sits for a few hours, you start it and the idle jumps up to ~2100rpm instantly, stays there a few seconds and falls to ~1500 rpm. All started after I cleaned the throttle body, unsure of the cause. I've checked the ISC motor and the TPS (both fine) and I don't wanna mess with the idle screw on the TB. I believe its a temp issue. The other day, it was 90 in Fontana and I went to start after it sat for 7 hours and the problem wasn't as bad. It didn't jump as high or stay very long.

I'm going to check the IAT and ECT sensors. I think the cold start injector might be firing a little too long when the thing is cold. I've heard bad ECT sensors can cause problems when the engine is dead cold and work fine the rest of the time. Depends on the thermistor setting (NTC/PTC). I'll keep you posted.

04-16-2006, 11:32 PM	#7 (permalink)
CTD20 Cornerworker Join Date: Mar 2006 Location: Simi Valley, CA Posts: 2 Thanks: 0 Thanked 0 Times in 0 Posts iTrader Rating: (0/0% )	Similar issue - 91 5s My 91 NA does something similar. After it sits for a few hours, you start it and the idle jumps up to ~2100rpm instantly, stays there a few seconds and falls to ~1500 rpm. All started after I cleaned the throttle body, unsure of the cause. I've checked the ISC motor and the TPS (both fine) and I don't wanna mess with the idle screw on the TB. I believe its a temp issue. The other day, it was 90 in Fontana and I went to start after it sat for 7 hours and the problem wasn't as bad. It didn't jump as high or stay very long. I'm going to check the IAT and ECT sensors. I think the cold start injector might be firing a little too long when the thing is cold. I've heard bad ECT sensors can cause problems when the engine is dead cold and work fine the rest of the time. Depends on the thermistor setting (NTC/PTC). I'll keep you posted.