Vstahl

hey all,
my jeep has a high idle that is making it undriveable. I have replaced the idle air control valve and have sprayed the vacumn lines with carb cleaner to see if I had a vacumn leak with no succcess. any other ideas?

it is an 89 cherokee 4.0 with a stock motor, no modifications.

ZINGGG

https://www.cherokeeforum.com/f2/free-quick-fix-41821/

Try this. Takes only a minute to do

Vstahl

anyone else have an idea why my engine idle is so high?

ZINGGG

There could be many reasons. Bad TPS, bad exhaust leak, bad o2 sensor, etc. Make sure the vaccum line that attaches to the MAP sensor is in tact and is not restricted. Also, give your throttle body a good cleaning while you're over there.

You have a Renix so I'm sure DFlint or cruiser will be jumpin in here soon.

cruiser54

Most likely the TPS is going south on you. You'll need a multi-meter to check it out.


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 bodyand 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

NorCalJeep

Your TPS sounds like it could be the culprit.

Vstahl

Cruiser54,
thank you for the info thus far. Could I get that instruction sheet on the sensor ground repair?

cherokeelaredo'90

Check your exhaust header bolts mine were a little lose and tightening those up as well as cleaning the iac and mat sensors brought my idle down. I should probably replace my iac because it seemed pretty gummed up but it still idles fine and runs so whatever.

cruiser54

Find your Intake Air Temp sensor. It's the sensor just to the rear of the throttle body, has 2 wires, and screws into the intake manifold.
Where it's connector plugs into the harness you will see that one of the wires on the harness side　is brown with a white stripe. Follow the brown with white stripe wire back into the harness. You'll have to open up the split-loom plastic sheathing to follow it. It will come to a splice with 2 other brown with white wires with duct tape over them. They're from the TPS and the CTS. The 3 wires will be　 spliced to a single wire headed toward the C101 connector if you have an 87 or 88. If you have an 89 or 90, you do not have the C101 bulkhead connector.
　
Now go to the MAP sensor. Follow the brown with white wire into the harness from there. You will find a splice with 2 more brown with white wires with duct tape over them. At the splice you will find the 3 wires connected to a single brown with white wire going toward the C101, or just along the firewall towards the engine if you have an 89 or 90. Along with the MAP sensor that you traced, they are the ECU sensor ground port and the diagnostic connector on the passenger inner fender.
　
You now have 2 sets of 3 brown with white wires, one near the firewall and one near the engine.
　
Cut the splices out of each set of wires eliminating not only the crappy factory splices, but also the single wire between them. Bring both sets of 3 wires together. Solder the 2 sets of wires together and insulate them properly with tape or shrink tubing.
　
Zip-tie up your new sensor loom to allow for engine movement.　I prefer to cover it with some new split-loom or wrap it neatly with electrical tape when done.
　
　
Revised 03-09-12

highmileage

The back bolts to the intake can and have a habit of backing off, took me about two days to find the problem after checking the vac lines TPS and associated sensors

belvedere

Did you spray carb cleaner around the intake manifold gasket?

Vstahl

cruiser54,
i just finished the ground wire fix and have now tested the tps. The readings I found were... 4.87 for my reference voltage and .72 for my output voltage. So I adjusted as you said to bring it to .8279 voltage. Then I started and it reved a high idle but not nearly as bad as before. So I tested the reading with the motor running and it is at .85 to .86 , It did not hold at the .8279. So would that mean I need to replace TPS? Also, on a side note... after messing with the volt meter for awhile testing as it was running a high idle I unplugged the TPS and then replugged it. The idle came down exactly as it should. So again, replace TPS?

cruiser54

Probably a good idea to replace the tPS and adjust the new one properly.

Vstahl

ok, will do tomorrow when the part gets in and I will let yall know how it comes out.

Vstahl

hey cruiser54,
thank you for the help last week on the TPS. Seems like I am chasing a ghost around this jeep. After I did the grounding fix you explained and adjusted the TPS everything has run like a champ. perfect start ups, great idle, everything.
Now this morning, a no start. Cranks over like a champ, but nothing. Very similar to when my CPS went south a few years back. I am guessing it is the same thing. Is there a way to test it effectively? any further instructions would be great.