worldsk8ter55

having an issue with my truck wen i start it its idles up to like 3grand and stays there, till ur turn it off. doesnt do it all the time but i have no clue what it is

CherokeeInAZ

clean IAC motor or replace it. You have a electric motor that controls the idle.

Gee oh Dee

X2

Small chance of a few other things, but most likely IAC.

kottobahn

I've had the same problem with my 89. I've been trying to chase it down for about a year now. I've replaced almost every sensor including IAC and tested the remaining ones. When mine's at operating temp it idles at around 1800. I can unplug the IAC and it has no effect on the idle. I have tried disconnecting various sensors and vaccum lines to see what effect it had. A few sensors killed the engine but when I disconnected the vaccum hose to the MAP sensor the idle dropped to about 850 rpm's. Anyone have a clue?

hearsedriver

May have a small vacuum leak not to sure.

DFlintstone

kottobahn, I followed a thread a while back, guy tried everything. Finally he went after the factory set, no adjustment needed, idle stop screw. Guess it should be set so the butterfly can't hit the throttle body. Hitting the concealment plug off center with a punch was mentioned. Have you all checked for vacuum leaks everywhere and around the intake manifold with a can of carb cleaner or quick start? A SHORT SHOT on a leak will make the rpm change.

CHEROKEEXJ1995

Okay I had the same problem on my 95 Cherokee. Ur throttle may be stuck a little bit or in my case my computer was going bad. Just thought I'd let ya no!

worldsk8ter55

thanks guys iv been trying to trouble shot this problem for awhile now just cant seem to find the problem, tried sensors, i checked for leaks. i ordered a new IAC today im hoping that solves my problems. iv been asking around to see what it is and everyones giving me the same answers so ill try it out

JohnWongFat

I had the same problem and mine turned out to be an exhaust leak. Spray some starter fluid along the exhaust manifold and listen for RPM changes. For some reason when I hit mine, the engine bogged down really badly. Found that the PO sheared off one of the bolts that hold the exhaust manifold on and the one above it was super loose. I tightened it down and it fixed my problem.

kottobahn

I saw the thread about tightening the manifold bolts. I started spraying starter fluid on the manifold then, stopped and realized I'm spraying one of the most flamable fluids on my engine. I did tighten all the bolts. One on the bottom was loose enough to spin the washer. Still no change. I found a vaccum leak which I fixed. I keep hoping something will work.

I read on another thread about being careful with your IAC not to pull on the pintile because it will ruin it. I noticed when I installed the new one the pintile was firmly in it's recess. I pulled on it very cautiously to see if it moved and I couldn't get to move at all. Could it be defective?

cruiser54

Idle flare like that is sometimes the TPS. It is adjustable on the 87 to 90 models, or it could be faulty. . A bad sensor ground circuit can also cause the high idle.
Try this: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: 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.
If you see more than 1 ohm of resistance 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.
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. 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.