i have a 1990 4.0 stock cherokee automatic. I have a weird problem with the idle that does not happen all the time. I was driving home, came to a stop light and and when I hit the brakes the truck stayed at about 2000 RPM. I through it in neatral and it jumped to about 3000rpm and I could not get it to idle down.I turned it on and off several times with not luck, it hit about 3500 rmp at one point. it has done this several times in the past month. I cleaned the throttle body and all the sensors hooked to it. I have not had this problem again, but it seems to still be idling high. about 1200 to 1500 in park around 900 to 1000 in park. the weather is usually damp or colder when it has happened. is there any sensors i should check. truck has about 216000 miles on it.

 

When My 88 did the high idle thing I unpluggsd the tps and plugged it back in ,that usually dropped the rpms down to idle. I then had to change the tps do to it going bad. You can try it to see if it helps .

 

TPS or IAC valve most likely.. Put a code reader on there and see what the deal is.. Even if the CEL isn't on...

 

Could be a vacuum leak. Check vacuum hoses and connections to the manifold.

 

MAP sensor can do this also. Code reader will help find this issue

 

Renix--- no codes no cel.

 

Pull the IAC and gently clean it with some carb cleaner and a toothbrush. Fixed my crazy idle on my 88..also see if you hear a hissing from a vac leak..

 

. I cleaned the TPS and it still idles high. what does IAC stand for

 

Tps adjustment.. trust me. Mime dis the same thing. I adjusted it to spec and it still did it. I played with it a little .01 v at a time and found that .02 above the spec it always starts and idea down to 900 then after a few seconds isles down to 700.

 

the IAC is the idle air control sensor, it is attached to your throttle body right by your tps. If your throttle body was really dirty, and you didn't pull the iac off when you cleaned everything, that could be your issue. It is very quick and easy to do, and can not hurt if you clean it and it is not the issue.

 

I cleaned the IAC as well, didnt know what it was but it was dirty. it helped the idle some but it is still a little high. I will check all the other things. thanks for the help

 

Garuntee the tps adjustment.

 

They have code readers for pre obd2 they can read the obd1 code

 

Renix isn't obd anything. It doesn't store codes. There is a machine that will do real time diagnostics bit its very expensive.

 

At this point, my money's on the TPS. PM me with your email address and I'll send you simple instructions to test/adjust the TPS on a Renix.