Possible IAC or TPS problem?

As most of you with older cherokees have already experienced (or probably will soon), the reverse lights tend to stop working, or work infrequently, when put into the mentioned gear. With such a common problem, it was very easy to find a fix for this.....cleaning the NSS switch. After doing so (and also having ruined a completely good pair of shorts in the process) I decided I might as well go all the way, and grease my chassis, as well as clean out my throttle body. After finishing these tasks, I decided to take the jeep for a spin to see if I could notice any improvements in performance.

This is where I ran into a new problem. When I started the engine, it was running about 700 RPM faster at idle than normal. I assumed this was probably due to the throttle body cleaner I used, so ignored it thinking it would go away.......160 miles later it's still doing the same thing. I tried cleaning the IAC motor, which was quite dirty, and this didn't do jack. So I am now trying to figure out if either the IAC motor or TPS are shot. I'm pretty sure I know how to test the TPS for proper voltage readings, but I'm not exactly sure how to test the IAC motor. Any thoughts?

Thanks

My 89 revved to 3000+ often, even after repeated cleaning of the throttle body and the IAC. I finally spent the $57 to replace it and the problem went away, except occasionally upon startup w/o the AC on it revs what seems like 300-700 RPM above normal and then comes back down. Still looking for the culprit. Maybe you should check the TPS first and also, vacuum leaks would introduce air into the intake too. Wouldn't the engine respond to excess air into the intake the same as if the IAC were not extending its pintle as commanded? On top of that, such a leak-say at the brake booster hose or elswhere, would be a source of dirt into the engine.

Thanks for the response.

I replaced my IAC valve yesterday, and that didn't solve the problem. I also checked the voltages on the TPS, and they tested good... my only other option now I guess would be to check the wire connections on the IAC and TPS for corrosion, and check vacuum lines for leaks. If any one else has any suggestions, I'd be extremely appreciative.

There is one other thing I might note. There is a red vacuum line that goes to the tranny, starting from near the passenger side of the firewall. Could this line be a possible culprit for high idle speed? I think I may have pulled on it when I was removing the NSS switch. Thanks again.

i recommend buying the TPS and puting it on to see it if thats not your problem if its not you can always take it off and take it back and get your money back. i tested my TPS and it read fine around five volts, but i bought the new TPS put it on and now it idles fine now.

well, I am actually having a similar problem.. My xj has been idling around 1500, but eratically. Secondly, all of the sudden no cruise. Could these prbolems be linked. I assume the tps tells the ecu wehre the throotle is at, which adjusts the speed accordingly? One other thing, when starting in the morning, it must warm up, just throwing it into gear stalls her. hmmm... well i will start playing with it, if anyone has any suggestions they would be greatly appreciated.
thanks
carlton

When you say that the crusie is out, this does lead to a possible connection. Operation of the cruise control uses a vacuum cansiter. I think I have seen it on the passenger side upper firewall on another 89 with cruise. If the diaphram in the canister burst or the vacuum hose broke, then the servo that operates your throttle is disabled. The resulting vac. leak could also affect your idle. The test is to search out the leak, and failing to locate it, plug of the hose to the canister and see if this affects your idle.

You could also have some jammed up worn out throttle linkage parts. Better take a look or you'll be making like an Audi or Lincoln - "Unintended Acceleration"- especially if you shift into 4Lo and the throttle sticks at 3 grand.

By the way, my idle problem went away. My IAC instructions said the ECM would take a few miles to recalibrate with the new IAC.

I was wondering something about the TPS. The little lever on the TB side of the sensor that is caught by the adjuster bar on the actual TB... if you move that bar, is it supposed to make the car change its idle. I was just wondering, because mine doesn't.

Tripp,
This cruise control vacuum canister you are talking about... where is it in relation to the heater blower motor? On the passenger side of my firewall there is a blue vacuum line just kinda hanging there, not attached to anything. I always thought this was part of the A/C, and didn't mess with it. I doubt this is related to my idle problem, because it has been there for several years like this. I have had a problem with my vents changing though. No matter what setting I put the A/C on, it always comes out of the defrost vents on my dash. Kinda bugs.

Also, like cjwalker, my idle problem is erratic. In park or neutral, it's always at or over 1500 RPM, and every few seconds it revs up another 400 RPM or so, then goes back to 1500. I now have 40 miles on my new IAC, and it hasn't helped. Maybe disconnecting the battery for a minute to reset the computer would help? I already tried returning the IAC as well, and they wouldn't let me, so I don't wanna chance not being able to return the TPS.

Anyway, thanks to everyone for trying to help with this issue.