Chuck Norris

Ok heres my problem. I have an 88 xj. I had a rough idle, but i changed my spark plugs and that seemed to fix that. How ever a week later a new issue arose.

Every so often when i drive it (and i haven't been driving it much because of this) it starts sputtering like i'm running out of gas, how ever i have half a tank. I drove it around my block a good twenty times in a big loop, until it did it again up my street. I push the gas pedal and it sputters, If its just sitting at idle there's no sputter. Or if its in park just idling it dies after a few minutes. did it twice today on me.I had the fuel pump changed last year around this time because it died on me on the freeway.

has any one else experienced this or maybe have suggestions. I haven't done a compression check yet, been so busy with work. but if i gets some time maybe this weekend i'm going to give it a go. It has a little over 250k miles on it. almost all of which were put on by the previous owner

tjwalker

1. Finish your tuneup with new plug wires, distributor cap, rotor, fuel filter and air filter

2. Clean your throttle body and idle air control. They are a common cause of problems as they get carboned up over time and miles. The ho-to is below.

3. Test AND adjust your throttle position sensor. Your TPS is adjustable. More on that below.

4. A compression test on a 250k engine is never a bad idea. A good snapshot in time of the internal condition of the engine. Spec for the 4.0 is 120-150 psi, with no more than a 30 psi variation between cylinders.

5. Verify fuel pressure. Must be done with a gauge. For an 88, you should have 31 psi at idle. Then disconnect the vacuum line going to the fuel pressure regulator and the pressure should jump to approx. 39 psi.

Good luck!
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The Idle Air Control (IAC) is mounted on the back of the throttle body. The valve controls the idle speed of the engine by controlling the amount of air flowing through the air control passage. It consists of a stepper motor that moves a pintle shaped plunger in and out of the air control passage. When the valve plunger is moved in, the air control passage flows more air which raises the idle speed. When the valve plunger is moved out, the air control passage flows less air which lowers the idle speed. Over time and miles, the IAC can get carboned up which can have an adverse affect on idle quality. Cleaning the IAC may restore proper function and is an easy procedure to perform and good preventive maintenance so it is never a bad idea.

CLEANING THE JEEP 4.0 IDLE AIR CONTROL

Remove the air filter cover, associated hoses and the rubber boot that goes from the air filter cover to the throttle body. Remove the IAC with a torx driver (2 bolts; one can be kind of hard to get to)

“Gently” wiggle out the IAC from the throttle body. Gasket on the IAC can be re-used if it is not damaged

Clean the IAC with a spray can of throttle body cleaner; inexpensive and available at any place that sells auto parts. Throttle body cleaner is recommended rather than carburetor cleaner as it is less harsh, safe for throttle body coatings and is best for this task. Use cleaner, a rag and a toothbrush and or Q-Tips. Be gentle; don’t twist or pull on the pintle that protrudes from the IAC as it is fragile and you could damage it.

Thoroughly spray clean and flush where the IAC seats in the throttle body with the same spray cleaner

It is also a good idea to clean the entire throttle body itself, the butterfly valve inside of the throttle body and all associated linkage as long as you have things disassembled

Reinstall IAC and check idle quality
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RENIX TPS
(Thanks to Joe Peters from NAXJA for this information)

MANUAL TRANSMISSION:

RENIX manual transmission equipped XJs have a three-wire TPS mounted on the throttle body. This manual transmission vehicle TPS provides data input to the ECU. The manual transmission TPS has three wires in the connector. Wire "A" is positive. Wire "D" is ground. Remove the three-wire connector from the TPS. Key ON, measure voltage from "A" positive to "D" ground. Note the voltage reading--this is your REFERENCE voltage. Now, reconnect the three-wire connector to the TPS. Key ON, back-probe the connector at wires "B" and "D". Measure the voltage. This is your OUTPUT voltage. Your OUTPUT voltage needs to be seventeen percent of your REFERENCE voltage. Adjust the TPS until you have achieved this percentage, if you can't achieve the correct output voltage replace the TPS and start over.

AUTOMATIC TRANSMISSION:

RENIX automatic transmission equipped XJs have a TPS with two connectors. There is a three-wire connector, same as the manual transmission vehicles have, and it is tested the same as the manual transmission equipped vehicles--FOR ENGINE MANAGEMENT RELATED ISSUES. However, the automatic TPS also has a four-wire connector. For the automatic transmission equipped vehicles the four-wire connector provides data to the TCU. Disconnect the four-wire connector. Key ON, measure voltage between "A" positive and "D" ground. Note the voltage. This is your REFERENCE voltage. Now, reconnect the four-wire connector to the TPS. 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. 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. If you have TRANSMISSION issues check the four-wire connector side of the TPS. If you have ENGINE issues check the 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.

Chuck Norris

Thanks for all of the info. its very useful.

I've already done the tune up prior to this post. new wires, spark plugs, oil change etc. I had even changed my IAC because i thought it was the root cause of my idle issue. I cleaned my throttle body a little, but i was unsure if spraying alot of throttle body cleaner in it would hurt it or now. it could probably stand a better cleaning.

I just got a new CPS yesterday, it arrived from rock auto. Gonna swap that out, run the compression check, and see if i could better clean my throttle body tomorrow morning when i get home from work.

I'll let you know if that fixed it