XcherokeeJ

Right when I start my XJ, when I step on my gas pedal the RPM's drop down and will sometimes stall out my jeep. I do drive a five speed. This only happens when I first start my car no matter what the temp outside. After driving in first to almost redline pretty much fixes the problem. Then after it has "warmed up" it will not do this again until after it has shut off and cooled down.

I have been thinking about changing the spark plugs but may not be the problem. It almost seems like there is too much gas going in to begin with. Thanks in advance!

Radi

I wonder if your IAC is sticking until it warms up a bit? Any sign of vacuum leaks? Intake bolts all snug?

XcherokeeJ

What is the IAC? Not familiar with that one. I will have to double check for leaks and snuggness when it is light out. I always remember when it is dark out or I am at work...

Roler

IAC would be one of my choices too if it would stall while idling or right after startup. Def worth a clean. However, if the gas is pressed (letting more air in) it stalls, wondering if the fuel delivery has issues therefore? But sounds like a thermal related issue. Even things like the CPS could be involved, so needs somewhat systematic approach.
Btw a new tune up is never a bad plan, if not been done recently. Gets that out of the way.

cruiser54

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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

XcherokeeJ

I will definitely get some deep cleaning done today on the TB and IAC. I will keep you posted on how that goes. Thanks so much for the input!

cruiser54

Here's a homework assignment for you. Needs to be done, it's easy and worth it.

Renix Ground Refreshing
The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of driveabililty issues, wasted time, and wasted money replacing unnecessary components.
The components grounding at the dipstick tube stud are:
Distributor Sync Sensor, TCU main ground, TCU "Shift Point Logic", Ignition control Module, Injectors, ECU main ground which other engine sensors ground through, Oxygen sensor, Knock Sensor, Cruise Control, and Transmission Sync signal. All extremely important stuff.
The factory was aware of the issues with this ground point and addressed it by suggesting the following:
Remove the nut holding the wire terminals to the stud. Verify that the stud is indeed tightened securely into the block. Scrape any and all paint from the stud’s mounting surface where the wires will attach. Must be clean, shiny and free of any oil, grease, or paint.
Inspect the wire terminals. Check to see that none of the terminals are crimped over wire insulation instead of bare wire. Be sure the crimps are tight. It wouldn’t hurt to re-crimp them just as a matter of course. Sand and polish the wire terminals until clean and shiny on both sides. Reinstall all the wires to the stud and tighten the nut down securely.
While you’re in that general area, locate the battery negative cable which is fastened to the engine block just forward of the dipstick stud. Remove the bolt, scrape the block to bare metal, clean and polish the cable terminal, and reattach securely.
Another area where the grounding system on Renix era Jeeps was lacking is the engine to chassis ground. There is a braided cable from the back of the cylinder head that also attaches to the driver’s side of the firewall. This cable is undersized for it’s intended use and subject to corrosion and poor connections at each end.
First off, remove the cable end from the firewall using a 15mm wrench or socket. Scrape the paint off down to bare metal and clean the wire terminal. Reattach securely.
Remove the other end of the cable from the rear of the head using a 3’4" socket. Clean all the oil, paint and crud from the stud. Clean the wire terminal of the cable and reattach securely.
A suggestion regarding the braided cable:
I prefer to add a #4 Gauge cable from the firewall to a bolt on the rear of the intake manifold, either to a heat shield bolt or fuel rail bolt. A cable about 18" long with a 3/8" lug on each end works great and you can get one at any parts store already made up. Napa has them as part number 781116.
A further improvement to the grounding system can be made using a #4 cable, about 10" long with 3/8" terminals at each end. Attach one end of this cable to the negative battery bolt and the other end under the closest 10mm headed bolt on the radiator support just forward of the battery. Napa part number 781115.
　
　
If you want to upgrade your grounds and battery cables in general, contact Jon at www.kelleyswip.com. He makes an incredible cable upgrade for a very reasonable price.
　
Revised 11-28-2011

Renix Jeep C101 Connector Refreshing
　
The C101 connector on 1987 and 1988 Renix Jeeps was a source of electrical resistance when the vehicles were new. So much so that the factory eliminated this connector in the 1989 and 1990 models. The factory recommended cleaning this connector to insure the proper voltage and ground signals between the ECU and the fuel injection sensors. We can only imagine how this connector has become a larger source of voltage loss and increased resistance over a period of almost 25 years. The C101 connector needs to be cleaned at least once in the lifetime of your vehicle. Chances are it’s never been done before.

Almost every critical signal between the engine sensors, injectors, ECU, and some to the TCU, travel this path through the C101 connector.
The C101 connector is located on the driver’s side firewall above and behind the brake booster. It is held together with a single bolt in it’s center. To get the connectors apart, simply remove the bolt and pull the halves apart. You will find the connector is packed with a black tar like substance which has hardened over time.
Take a pocket screwdriver or the like and scrape out all the tar crap you can. Follow up by spraying out both connector halves with brake cleaner and then swabbing out the remainder of the tar. Repeat this procedure until the tar is totally removed. This may require 3 or more repetitions. Wipe out the connectors after spraying with a soft cloth.
If you have a small pick or dental tool, tweak the female connectors on the one side so they grab the pins on the opposite side a bit tighter before bolting both halves back together.
　
Revised 07-17-2012
Cruiser’s Renix ECU Connector Refreshing
Many times when other fixes have failed, it becomes necessary to eliminate the ECU to harness connections as a cause. This requires removing the ECU.
Up under the dash, to the right of the steering column is the ECU. It is held in by three 10mm headed bolts to a bracket. It’s most easily removed using a ratcheting wrench but a socket will work.
Once you get the ECU down, unplug the two harness connectors from it. Visually inspect the connectors and pins.
Using a good quality electronics cleaner, liberally spray both of the harness ends and the ECU pin area.
Now, take a small pick or a dental tool and go to the harness connectors. Using the tool, tweak each female receptacle in the harness plugs so they will grasp the ECU pins more tightly.
Plug the harnesses back on to the ECU and reinstall it. I usually only use two of the bolts because the third is a bear.
Revised 07/11/12

XcherokeeJ

I think i may have found the problem. Something was not plugged all the way in. But when it is plugged in the engine revs at 2k rpms.











That is what was unplugged. Sorry if there are too many pics. Sending this from my phone. Thanks!!

hankthetank

tps

cruiser54

Check out your TPS using this. I'm assuming the flat 3-wire was disconnected?


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 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 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. 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 flat 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 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 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.
Revised 08-27-2012

F1Addict

...and you're missing a bolt on your fuel rail.

XcherokeeJ

I did some cleaning today on the TB and the IAC, assuming that is what is next to the tps... Engine still revs at 2k rpms and will have to check out ground connections later. Just found out that I have a antifreeze leak right out of the housing where the tube connects.

cruiser54

Yeah, do all the stuff in post #7 first.

Where's this anti-freeze leak?

XcherokeeJ

It is the far left tube from the thermostat housing as you are looking at the Jeep from the front. It is where the sincher is sinching the tube (for the lack of better terms). I also found, I think, a black box attached on the fire wall on the driver side that seems to be a huge plug that is completely gummed up, which seems to be connected to the throttle body. The location cannot get any higher or closer to the hood. What is this and how would I clean it?

cruiser54

That "black box" is more than likely the C101 connector I refer to in post #7.