1987 Laredo 4.0 200,000 + miles.

Last summer i started having a high rpm issue. I would start it, and it would race at 3200 rpm. Sometimes it would go back down to idle after a few minutes and sometimes it would stay up there for a long time while driving around. Sometimes would be normal, than stop for gas or something and back up to 3200 when I start it. It did this at random times, but during the winter it never did it. This summer it started doing it again. It is random though, some days it does not happen at all.

So what is strange is 1. does not occur during cool weather. 2. totally random occurences.

Any ideas?
Thanks

 

Try adjusting your tps,or cleaning the iac,both on the throttle body in the front,my has done the samething before,it is quite common. Why it chooses hot weather vs cold might have to do with resistance when it is hot,all those little electrons slowdown,just a thought.

 

Idle stepper motor (iac) stuck, replace.

 

Thanks to both of you, will replace the IAC first and see what happens.

 

Replace the throttle positioning sensor

 

are you saying you replaced the tps,or are you asking if you should?

 

For now I took off the IAC and cleaned it, and then I checked the TPS and it was within .5% of spec, so I left it alone. Troy I don't believe I have a throttle position sensor becasue apparently I have multi point fuel injection system rather than throttle body fuel injection (according to Chilton). If cleaning the IAC doesn't do it I'll try replacing it.

Thanks again, will report back when I know something.

 

my 87 MJ used to do that... I called it "redneck cruise control"

 

TPS=throttle position sensor, equipped on multipoint fuel injection.
DualTPS in case of automatic transmission.

 

I have multi point fuel injection also and my tps went bad so I replaced it and all is well. My motor would idle at 2500 to 3000 rpms . Works great now . Good luck.

 

So far so good after cleaning the IAC. But if the issue does come back now I know what else to try, so thanks for all the advice.

 

so was it the iac?