Nakedginger

Hey all,

So I have been having a strange problem with my 90 XJ. First off some background info. It is a 1990 XJ, it has a straight six in it, and it is the Renix system. The problem I am having is, I will start my XJ and everything will be fine. A few minutes down the road though it starts having a idling issue once I take my foot off the pedal. When I do take my foot of the gas the engine will drop in RPM's, and stall. I had this issue a few weeks ago and resolved it by replacing the throttle position sensor.

A couple weeks down the road (today) I was driving to work when a few minutes after starting it seemed as if I gave the jeep gas but it wasn't going faster. It then took off but when I let off the gas the RPM's went down and the engine stalled. Now its doing the same thing as it did a few weeks ago. Once the engine has run for a few minutes the engine wont stay idling if I take my foot of the gas

I will be testing the new TPS to make sure it wasn't a faulty one as well as going through relays and grounds. If its not that, does anyone have any ideas to what the problem could be centered around? Feel free to ask questions and I will appreciate any input.

Thanks!

-Jonathan

Nakedginger

I checked the TPS and the voltage is where its suppose to be. The outgoing voltage with the ignition on is 80% of the voltage going into the sensor. Ill be digging into it more in the next couple days. For now its time to walk!

jake92

Hows the throttle body?

cruiser54

You're testing the TPS on the "trans" side while looking for an issue on the "engine" side.

This should help. Make sure your throttle body and IAC are clean first.

Ever click on the pink link in my signature for the write-ups I've done to address odd Renix issues?

Do the sensor ground test outlined below in the TPS instructions first.


RENIX TPS ADJUSTMENT
Before attempting to adjust your TPS be sure the throttle body has been recently cleaned. It's especially important that the edges of the throttle butterfly are free of any carbon build-up.
IMPORTANT NOTE: With the Key OFF, and using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connector of the TPS. The letters are embossed on the connector itself. Touch the black lead of your meter to the negative battery post. Wiggle the wiring harness where it parallels the valve cover and also over near the MAP sensor on the firewall. If you see more than 1 ohm of resistance, or fluctuation in your ohms reading, some modifications to the sensor ground harness will be necessary. The harness repair must be performed before proceeding. I can provide an instruction sheet for that if needed.
MANUAL TRANSMISSION:
RENIX manual transmission equipped XJs have only a flat three-wire TPS mounted on the throttle body and it provides data input to the ECU. It has three wires in the connector and they're clearly embossed with the letters A, B, and C. Wire "A" is positive. Wire "B" is ground. Key ON, measure voltage from "A" positive to "B" ground by back-probing the connectors. Note the voltage reading--this is your REFERENCE voltage. Key ON, back-probe the connector at wires "B" and "C". Measure the voltage. This is your OUTPUT voltage. Your OUTPUT voltage needs to be seventeen percent of your REFERENCE voltage. For example: 4.82 volts X .17=.82 volts. Loosen both T-20 Torx screws attaching the TPS to the throttle body and rotate the TPS until you
have achieved your desired output voltage. Tighten the screws carefully while watching to see that your output voltage remains where it is supposed to be. If you can't achieve the correct output voltage, replace the TPS and start over.
Sometimes, after adjusting your TPS the way outlined above, you may experience a high idle upon starting. If that happens, shut the engine off and reconnect your probes to B and C. Start the engine and while watching your meter, turn the TPS clockwise until the idle drops to normal and then rotate it back counterclockwise to your desired output voltage.
AUTOMATIC TRANSMISSION: RENIX automatic transmission equipped XJs have a TPS with two connectors. There is a flat three-wire connector, same as the manual transmission vehicles have, and it is tested the same as the manual transmission equipped vehicles, as outlined above—FOR ALL ENGINE MANAGEMENT RELATED ISSUES.
However, the automatic TPS also has a square four-wire connector, clearly embossed with the letters A,B,C, and D. It only uses three wires and provides information to the Transmission Control Module. THIS SQUARE FOUR WIRE CONNECTOR IS USED FOR TRANSMISSION/SHIFTING RELATED ISSUES ONLY. Key ON, measure voltage between "A" positive and "D" ground. Note the voltage. This is your REFERENCE voltage. Back-probe the connector at wires "B" and "D". Measure the voltage. This is your OUTPUT voltage. Your OUTPUT voltage needs to be eighty-three percent of your REFERENCE voltage. For example 4.8 volts X .83=3.98 volts. Adjust the TPS until you have achieved this percentage. If you can't, replace the TPS and start over. So, if you have an automatic equipped XJ your TPS has two sides--one side feeds the ECU, and the other side feeds the TCU.
FOR AUTOMATIC TRANSMISSION RELATED ISSUES: Check the square four-wire connector side of the TPS.
If you have ENGINE ISSUES check the flat three-wire connector side of the TPS.
For those with a MANUAL TRANSMISSION--the TPS for the manual transmission XJs is stupid expensive. You can substitute the automatic transmission TPS which is reasonably priced.
Revised 09-22-2012

DFlintstone

Last month a guy in my town had an 89 that could die at every stoplight. I went straight to the CPS and saw he had only .1 ACV. I'm surprised it ran at all!

Nakedginger

Thanks for the input! Ill be checking the TPS on the engine side like you said cruiser54. Ill also be checking the IAC and the status of the throttle body. While Im at it I mine as well check the voltage for the CPS. You guys have given me something to go on! Again, thanks.

Nakedginger

Well I tested the TPS on the engine side and it has the proper ratio of 17% between the incoming voltage and the outgoing. I also took the ICA sensor out, cleaned it, and also cleaned the housing it sits in. I put all that back together and went for a drive. If I keep the motor at higher rpms (like around 1500-2000) and then take my foot off the gas I cant get it to fail. Although when the motor starts getting warm (like around 150 degrees) if I have the rpms around 700-1000 rpms and then let off the gas, it will stall. This only happened when i barely gave it gas and also when it was 150 degrees and above. I still need to test the CPS and possibly clean the throttle body more.

Just wanted to put up an update. Again thanks for the input you all have given!

Nakedginger

So I thought I would put a post up with a conclusion. In the end I cleaned the throttle body along with the IAC sensor. Between cleaning each of them she is running strong now!

cruiser54

Well, imagine that!! Regular maintenance gets performed and we don't need all sorts of sensors, ECUs, PCMs, catalytic converters, and so on.

Excellent job!!!

DFlintstone

You haven't checked your CPS?

Nakedginger

Yeah, I didn't think to clean the throttle body ever since I bought the XJ. Guess I pushed that maintenance task to its limit.

Thanks again for all the help! I do greatly appreciate it.