Jeep With High Idle and Cutting Off

I have a 1987 Jeep Wagoneer 4x4 with 4.0 I6. The Jeep is driven everyday.

1. I have a problem with the jeep having a very high idle. The high idle starts right after the jeep is started, but it does not occur all of the time. The high idle can occur when the Jeep is cold in the morning (normal), but also after the Jeep has been driven 40 miles shut off and left to sit 10 minutes and then started back again. The high idle does not happen all of the time, but has been known to happen in all weather conditions rain or shine.

2. I also have a problem with my jeep just cutting off after it has been running for well over thirty minutes and brought up to operating temperature. I will come to a stop sign or light. The engine will be running quiet and smooth at a low rpm. It sometimes makes me wonder if the engine is running, but I know that it is by the voltage output gauge and oil pressure gauge. As I start to accelerate from a stop, the engine will just cut off and then things are really whisper quiet. Also this problem does not happen all of the time.

I do not know if these two problems are related, but I wanted to give as much information as possible. Does anyone have any ideas where I might start looking for the cause of these problems? Thanks for the help.

The occasional high idle at startup thing, is a common sickness (usually on a warm motor). Don´t really know of anyone, who has successfully stopped it completely and forever (mine stopped over reving at startup for a week after some fairly major cleaning and adjustments, then started doing it again this morning ). Jeep did a recall to install a gizmo, so you couldn´t shift into drive, without your foot being on the brake pedal, don´t know for sure, but have my suspicions, this was there solution to the problem.
A clean IAC piston and seat, is a good place to start (a sticky IAC seems to be more common on a cold motor). Making sure your vacuum lines are in good shape is another, especialy the large vacuum line running to the vacuum resivoir, behind the right front fender. A major vacuum leak will often cause a very high idle, a moderate to small leak, often causes, the idle to hunt (up and down). A vacuum leak can cause faulty and/or conflicting imputs to the ECU from the 02 sensor, the TPS and other sensors, that seems to cause the ECU, to have trouble, making the IAC function properly.
If your vacuum lines are in good shape and the IAC is clean and functioning, a faulty sensor is a possibilty. I´m gonna swap out my O2 sensor and see what happens, it´s past time for a change anyway.

I actually have more Renix IAC troubles when HOT than cold. Idling fast after shutdown cook-off seems to mostly be sign of IAC weakness. Remember, the ECU parks the IAC in open position for the next restart when shutdown. Most stores offer 90 warranty on the IAC so if I get a couple HOT high idle events I'll return it and get another. I finally seem to have one that never acts-up HOT.

But, that's assuming a clean TB and "properly installed" IAC. Easy to get that o-ring botched and then the pintle is crooked in the TB. That will give 'em fits too. Good adjustment of throttle butterfly and TPS seems to help too. Ditto all vacuum lines and devices.

Check out the CPS connector running down the firewall behind the head on the drivers side for your crank no-start problem. They are common problem with this era.

Erratic idle - dropping really slow and then bumping-up again seems to have a lot to do with the 02 sensor. $52 last week and my mileage and idle are back to normal.

Few things come to mind since yours is an 87..........Open the hood and look to the right side of the firewall by the manufacture info sticker,you will see what is called a bulkhead,this is where alot of probs with wiring connections happens....this big wiring connector they did away with after your year because of all the resistence,corrosion etc that happens at this connection...the fix for this is to trace all the wires from your TPS that go to the bulkehead,what you want to do is cut the corresponding wires on each side of the bulkhead and solder and heatshrink the wires together by corresponding circut.....you want to bypass the bulkhead connection point for these wires...also if I remember right,there was like 15 superceeded Renix engine controllers I was installing back in the day to correct idle flash as its called...this is just the tip of the iceberg,,,do the tps wiring bulkhead bypass first and see if it helps......then comes a few other things aperwork,next will be CPS patchkit and high alt CPS with proper adjustment technique

Rags :wave:
www.arizonajeepextreme.com
Naxja member #114


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wbelk7777 said:

I have a 1987 Jeep Wagoneer 4x4 with 4.0 I6. The Jeep is driven everyday.

1. I have a problem with the jeep having a very high idle. The high idle starts right after the jeep is started, but it does not occur all of the time. The high idle can occur when the Jeep is cold in the morning (normal), but also after the Jeep has been driven 40 miles shut off and left to sit 10 minutes and then started back again. The high idle does not happen all of the time, but has been known to happen in all weather conditions rain or shine.

2. I also have a problem with my jeep just cutting off after it has been running for well over thirty minutes and brought up to operating temperature. I will come to a stop sign or light. The engine will be running quiet and smooth at a low rpm. It sometimes makes me wonder if the engine is running, but I know that it is by the voltage output gauge and oil pressure gauge. As I start to accelerate from a stop, the engine will just cut off and then things are really whisper quiet. Also this problem does not happen all of the time.

I do not know if these two problems are related, but I wanted to give as much information as possible. Does anyone have any ideas where I might start looking for the cause of these problems? Thanks for the help.

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I'm with Rags: the high idle is most likely TPS related. My Renix 1990 is on its third TPS, with high idle each time they failed. On your year, the TPS must be properly adjusted. The dealer does a better job with their equipment than I can do with a multimeter. The intermittent stalling is most likley a Crankshaft Position Sensor problem. Replacing the CPS solved this exact issue on my daughter's jeep (also 1990). Before replacing the CPS, you may want to try cleaning the connectors, since those can cause your problem. The ultimate CPS fix is the kit from the dealer which includes a CPS and a new connection wire that runs from the CPS to the computer, bypassing your old OEM wiring completely. I have this for mine. I bought the regular CPS-I should have bought the high altitude CPS, to make up for some wear in the distributor bushings (which retards timing a bit). The adjustable CPS and high altitude options are only for 4.0 engines up to 1990. The HO CPS is not adjustable, and there is no high altitude option either.

Years ago alot of peeps used to use these adjustable CP Sensors...They used to actually list these for Jeep 4.0...now they just list them as modified...these are Chrysler sensors that have the holes slotted for timing adjust...just match up connector specs and good to go for the HO peeps..............and If I do remember right,these will fit auto or manual trans.............. http://www.turbocity.com/advanced_s..._description=1&keywords=crank+position+sensor
http://www.turbocity.com/default.php?cPath=17_58

Rags :wave:

4xBob said:

I'm with Rags: the high idle is most likely TPS related. My Renix 1990 is on its third TPS, with high idle each time they failed. On your year, the TPS must be properly adjusted. The dealer does a better job with their equipment than I can do with a multimeter. The intermittent stalling is most likley a Crankshaft Position Sensor problem. Replacing the CPS solved this exact issue on my daughter's jeep (also 1990). Before replacing the CPS, you may want to try cleaning the connectors, since those can cause your problem. The ultimate CPS fix is the kit from the dealer which includes a CPS and a new connection wire that runs from the CPS to the computer, bypassing your old OEM wiring completely. I have this for mine. I bought the regular CPS-I should have bought the high altitude CPS, to make up for some wear in the distributor bushings (which retards timing a bit). The adjustable CPS and high altitude options are only for 4.0 engines up to 1990. The HO CPS is not adjustable, and there is no high altitude option either.

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