Well I normally have been getting all my tech questions answered with a simple search, you guys are always helpful, thanks!
That being said im having trouble with my jeep and can't find the answer.

Its an '88 XJ with 173k on it, had it since april. re-freshed grounds and replaced TPS due to high-idle problems on warm start-up. I also had done an ignition tune-up and more recently a fuel filter.
TPS cured the high idle problem, yet I seem to have a new issue since I replaced it, very hard cold starts, the jeep idles rougher, seems to be slightly down on power, and occaisional stalls when idling in gear cold (such as after coming to a stop, acts like someone shut off the key)
You guys think defective TPS? or maybe its fluke that this all happened after replacing TPS?

 

TPS's can go bad. I had a BWD brand go out 2 weeks after replacing it. Got from O's they do have a 1 yr. warranty but what a pain in the *** to think you have fixed your issue and have it return a short time later. I would suggest you retest it and do a sweep test to see if it is working correctly. Other than OEM I have heard the NAPA unit's that are @ $45 bucks seem to be the most reliable. You should also check your MAP sensor and all vacuum lines to make sure they are in good shape as well. Cracks or anything like that means they need to be replaced. It's also not a bad idea to check the IAC either if it's dirty or weak it'll cause idle issues as well.

Black89

 

I've been having the same problem with my 98, and occasionally my idle will shoot up to 2k when it's in neutral. I think I messed my IAC up when I cleaned it or something
I think i'm going to tune mine up change the o2s and see where that takes me

 

If the pintle on the IAC is dirty it can cause it to stick and hang up in the passage and if it's that bad the passages that the pintle controls the airflow to will most likely be gummed up as well. I had a 96 GC with a 318 in it a couple years back and the IAC was always an issue, about once a year I had to pull it and clean the crap out of the throttle body. It would only run if you kept your foot on the gas when the temps started to drop going into the fall.

Black89

 

A weak CPS can do that. You can literally test it in less time than it takes to boil coffee water ;


AC voltage CPS test; Small clips on the meter leads really helps.

Unplug the connector at the back of the manifold with wires going down to the bell-housing/cps.
Probe the two wires to the cps with the meter set on AC volts. (a 200 scale on mine).
Crank the engine and note the voltage. (jump it if your battery is low)

Mine somehow works with only .3 my wiring/grounds must be pretty spiffy. .5 seems to be a good mark. One article talked of .5 to .8. **Update, it soon failed. I installed Napa #css980 in my 90.** @.4 now.
If you click on my Signature Cruiser's Renix stuff it right on-top with more...

 

Make sure your sensor ground circuit is good. To set the TPS and check the ground circuit, use this, the "engine side" part:


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


Absolutely clean your throttle body and IAC. Check the tightness of your intake manifold bolts.

Courtesy of TJWalker:
--------------------------------------------------------------------
The Idle Air Control (IAC) is mounted on the back of the throttle body. (front for 87-90) 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

 

I'll admit I haven't had much chance to look at it further.. But just noticed a new symtom last night, now suspecting something spark related. I started it last night and got up to 45mph without much warm-up time like it usually gets.
Right after it shifted into O/D it has a dead miss that jerks the whole rig at cruise speed. Doesn't seem to do it when warm though

 

Dead miss or TC lockup? Still sounds to me like your TPS. It can wreak havoc on the shift points and make it feel like a miss. A jerk to me means tranny not shifting correctly due to a faulty TPS.

Black89

 

Well definitely haven't ruled out the TPS but it really feels more like the engine cutting out after it has already shifted into 4th and cruising at a constant speed. it didn't downshift or anything. I was thinking my CPS might be on its way out.. But who knows until I start poking around.

 

Hit Cruiser's link and do the CPS test as well..

Black89

 

Last time for plugs, wires, cap and rotor?

 

I was having similar issues with my 90. Turned out to be my EGR valve not sure how it all tied in but I disconnected it one day and drove around to test it out and everything worked fine. Hooked it back up and was wanting to stall again when I came to a stop sign/light. Replaced it and now it works fine.

 

Could be, but tune-up stuff has to be verified.

BTW, UPI tomorrow with a borrowed DeWalt impact......

 

Agreed. Basic tune-up first. Good luck at the UPI! Let me know if there is anything worth it to make the trip.

 

44 rear? ZJ discs?