scubadrew

Hello, first post here but have been lurking for quite some time, my problem is that on my 1989 Jeep Cherokee, whenever I am driving, and let off the throttle, if the RPMs are above 1250, they will jump down to 1250, say I'm going 40 mph and i let off the throttle, the rpms will jump down to 1250 in increments of about 100 until 1250 is reached, I have replaced the tps, cps and o2 sensor, this started after replacement of those parts, all napa premium or NGK. Any ideas? The P.O. was kind of ****ty and did a lot of stuff with the car (universal cold air intake, chopped exhaust so no downstream o2 or cat) etc. The car never did this before no parts were installed.

tjwalker

You mention specifically that this symptom did not occur BEFORE you replaced those parts. If that is the case then you have to look at the principle of "cause and effect" and you need to review work performed and parts installed.

For your situation/symptom, I think the throttle position sensor may be suspect. Did you adjust the new TPS after installation, that needs to be done with your vintage. If you have the old TPS, try reinstalling it and see if this symptom is resolved.

scubadrew

I have adjusted the tps to 80 percent of the input value, but Ill recheck it soon

tjwalker

Keep in mind that new parts can and do fail all the time. Ask any automotive technician that has been on the job more than a week for confirmation of this. That is why I asked if you still have your old TPS. Always save old parts for situations like this.

With exhaust mods, I'm assuming your check engine light is always on? Do a fresh pull for any codes and post them here for comment. There may be a clue in a new code that you aren't aware of if your check engine light is always on. As your 92 is OBD1, use the key-on-, key-off method shown below.
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Retrieving OBD codes on the Jeep Cherokee (XJ) OBD1 Models: 1991-1995

1) Start engine (if possible). Move transmission shift lever through all positions, ending in Park. Turn A/C switch on and then off (if equipped).

2) Turn engine off. Without starting engine again, turn ignition on, off, on, off and on within 5 seconds. Record 2-digit fault codes as displayed by flashing MIL.

3) For example, fault code 23 is displayed as flash, flash, 4-second pause, flash, flash, flash. After a slightly longer pause, other codes stored are displayed in numerical order. When MIL begins to flash fault codes, it cannot be stopped. Start over if count is lost.

NOTE: A "5-5" will always occur to signal the end of the sequence. Some will flash the "1-2" code indicating a recent battery disconnect even if you haven't done it. Ignore these two codes, and write down all others.

dmoe69

For the engine side the TPS is 17% of the reference voltage. If it is not one of the parts you replaced, it sounds like a ground problem.

lawsoncl

So the t/c is unlocking when it's supposed to now? Sounds like you fixed a problem rather than creating one.

cruiser54

First off, it never had a downstream O2 sensor.
You need to complete Tips 1,3,4, and 5 at www.cruiser54.com before wasting any more time and money with the parts cannon.
The correct way to set the TPS is also on the site, but the Tips mentioned above need to be completed first.