oldgraymule

Has any one experienced surging during normal acceleration.
My 1989 Jeep Cherokee, 4.0, 5-speed transmission, 204,000 miles has been starting to surg, feels like power on, less power, then power on again.
Other than that it starts fine after sitting for days.
I have no idea if it is fuel system related or ignition system.
Any help would be appreciated.

okcjeeper

IAC or maybe TPS.

BlueXJ

Renix my baby. TPS is getting bad. They are a reostat and just like the volume **** on a radio they wear and the resistance changes. Either replace it and recalibrate it or you may try just recalbration and that will get you by for a short time unless it is really badly worn.

oldgraymule

Thanks for the ideas.
I am new to this, so I am not up on the abbreviations for the various parts.
Renix is the computer in my Jeep.
TPS, throttle position sensor.
IAC,?
I got out my service manual and located the TPS.
I then went out to my Jeep and found it on the throttle body.
I am the original owner of this Jeep and I know that I have not replaced this part, so I guess I will try to get one on Monday.
This will be the first time that I have had to do any thing to the throttle body, except for the occasional cleaning of it.
Again thanks for this information.

okcjeeper

IAC is the Idle Air Control Motor..Also called the Idle Air Speed Motor....controls the idle speed but I dunno if RENIX has em...If they do it will be on the throttle body as well..I don't know jack about RENIX XJ's...

okcjeeper

IAC will look something like this...

jonb8

My 89 is doing the same thing but wasn't the tps, I'm starting to think crank sensor since I'm having a hard start proablem too.

BlueXJ

This will explain alot. Renix era Jeeps ended in 1990 thus the 87-90 are called Renix Jeeps. Not only were they on a particular ECU but their electronics were different than the subsequent years. This link will point out each sensor and describe how it works and how to diagnose it. You only need a cheap Digital multimeter. Your problem is likely different than jons because you do NOT have a hard start problem. The second most likely part would be the IAC but in the years that I have worked on Renix jeeps I have only seen one that was bad So I am still leaning towards the TPS. Read the info in this link and then try to diagnose the problem. Post up any further questions.
http://www.lunghd.com/Tech_Articles/...iagnostics.htm

COSXJFAN

Ya see boys!! Blue is a Renix NINJA!! You my boy Blue!!

BlueXJ

Thanks COS! I appreciate the vote of confidence.

oldgraymule

Well I did all of the test to see if the TPS was the problem, but the old TPS checked out.
It had 4.92 volts input and .83 volts on output.
I even checked the output volts by moving the lever in the back of the TPS and that looked good also.
I made a set of three jumper wires that I could take my readings from and that worked out just fine. I did this because I had no way of checking the voltage at the TPS connector. I disconnected the TPS connector and placed the jumper wires between the connectors so I could get a good connection for my probes on my meter.
I will drive it to see if I still have the problem.
Thanks Blue XJ for the link for the senors. It helped a lot.

BlueXJ

My pleasure. Hope that you find your culprit. I agree those TPS numbers look excellent for an older TPS in fact almost as good as a new one. You remember to get back to us with whatever you find your problem to be. That helps to broaden all our knowledge base.

oldgraymule

After adjusting the TPS the old Cherokee seamed to run fine.
Then I needed to use the A/C one day on my way home from work and the surging problem returned, but not as bad as it had previously been.
If I turned off the A/C the Cherokee seamed to run fine, but I do need to use the A/C at times here in New Mexico.
I purchased a new TPS and plan on installing it today, but I just wanted to get some input on this before I do the install.
I do enjoy seeing how long I can keep this Cherokee running, I just need some help in figuring out what the cause of the problem is and this is the place to get this information.
Thank you very much.

BlueXJ

I am still inclined to say your problem is TPS or IAC related. If you change to a new TPS and get the new one adjusted properly let us know if that was a cure for your surging.
Another thought came to mind. Do you do a lot of in town stop and go driving? If you do the O2 sensor may be carboned up as well and giving false readings to the ECU thus causing it to change the mixture. During those short surges you may smell a slight odor of exhaust that will smell funny. If that is the case take some electrical readings on your O2 sensor (yours only has one unlike the newer XJs) If that has a even slightly bad reading then that may also be your problem or at least part of it.
Blue

whowey

If he is going to be under the hood changing the TPS, why not pull the IAC clean it and check the pintle for correct operation?

If there is a ALOT of carbon build up in the TB it can certainly effect the IAC operation.