89Tonto Posted December 28, 2009 Share Posted December 28, 2009 Recently, I've had problems with a fast idle problem with my 89 MJ. Once I start the jeep up to warm up, the RPM's increase as the jeep warms ups. With no tach in the jeep yet, it appears it starts with a respectable 700-900 RPM's. After 10-15 mins of run time, it appears its running 2000+/- RPMs. Once the motor runs this fast, I shut the motor off and go in the house for 10-15+ minutes. When I come out and restart, everything appears to be OK. :doh: I've replaced the O2 sensor about 4 months ago. I cleaned the throttle body with TB cleaner the other day- a little oily. Maybe the idle air control valve is bad? Maybe a vacuum leak? Any thoughts? Link to comment Share on other sites More sharing options...
WBKrazy Posted December 28, 2009 Share Posted December 28, 2009 my guess would be the IAC on the throttle body.... Link to comment Share on other sites More sharing options...
Mike's Comanche Posted June 2, 2010 Share Posted June 2, 2010 How did that fast idle work out? I have the exact same problem, but the fast idle after warming up is closer to 2,500rpm. Link to comment Share on other sites More sharing options...
89Tonto Posted June 2, 2010 Author Share Posted June 2, 2010 I replaced both the IAC and TPS. The fast idle occurred back when it was cold outside. So far, so good. Good luck! Link to comment Share on other sites More sharing options...
Oizarod115 Posted June 2, 2010 Share Posted June 2, 2010 i had an odd fast idle just like this but it only went up to 1500-1750 or so, turned out to be a bad IAC Link to comment Share on other sites More sharing options...
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