89cherokee2gtmudy

88 comanche 4.0. I have ruled out vacuum leaks and manifold leaks. Randomly likes to idle at 3000 rpm and doesn't want to go down. Please help! Stuck out in the sticks right now.

freegdr

If its running drive outa the sticks b4 attempting any repairs.Running better than not running at all...

highmileage

Stuck butterfly?(the screw that looks like a idle screw is not for idle, it's for butterfly adjustment)
Bad idle air motor, or really dirty?
TPS way out of wack, or stuck(try giving it a soft rap with screwdriver handle)
Re-check your vac line assembly, mainly the block where they all come together, and the intake bolts underneath in the back.
Injector O-ring(s)?
Throttle body gasket?
All I got for now

cruiser54

TPS is probably taking a dive on ya.

Ever tested it or the sensor ground circuit?



RENIX TPS ADJUSTMENT

Before attempting to adjust your TPS, there are two things that need to be done.

1) 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.

2) With the Key OFF, and using the positive (red) lead of your ohmmeter, set on the lowest scale, 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.

TPS ADJUSTMENT FOR ENGINE ISSUES

Both RENIX manual and automatic transmission equipped XJs and MJs have a flat three-wire connector to the TPS which provides data input to the ECU. The three wires in the connector are clearly embossed with the letters A, B, and C. Wire "A" is positive. Wire "B" is ground. DO NOT UNPLUG THE CONNECTORS !! 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.

TPS ADJUSTMENT FOR AUTOMATIC TRANSMISSION ISSUES

RENIX automatic transmission equipped XJs and MJs 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 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. First off, DO NOT UNPLUG THE CONNECTORS !! Key ON, measure voltage between "A" positive and "D" ground by back-probing the connector. 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 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. The square 4 wire connector is just not used.
Revised 12-15-2013

89cherokee2gtmudy

Grounds test was done. Iac was just cleaned and still does it. Tps adjustment will be next.

cruiser54

Good plan. Remember to use the "engine" side.

89cherokee2gtmudy

It's a 5speed. Adjusted the tps which was way off. Still idles high. I took apart the iac which solved it for 2 rounds startup, but back to high idle. So I tore it apart again, started it with the iac unplugged. Plugged it in and the idle dropped to 800-900 so I unplugged it for now.

cruiser54

A new IAC MAY be in your future.

KD4315

Have you tired an iac or tps that you know is good? Sounds like your iac could be bad. The only other thing I would think would be bad grounds but you've already checked those.

89cherokee2gtmudy

I swore I had an extra iac laying around from my 89. I found just about every extra part I had from it but an iac.

89cherokee2gtmudy

I'm going to stock up on iac's and tps's from the junk yard.

KD4315

Risky move, especially with the Renix Jeeps where they're adjustable. Just make sure you're 100% confident that they're working and spot on. I have a late model XJ with a nonadjustable TPS and even those are enough to drive me to drink.

In other news I couldn't help but notice you have my dream truck listed in your sig.

89cherokee2gtmudy

My dodge? It's just a pavement pounder. Been commuting with if 100 miles a day. Has 2013 dodge rims, straight pipe and a rebuilt transmission that doesn't like cold weather.

89cherokee2gtmudy

I've had good luck with an iac for the 89. I only stock up on parts that look relatively new and that are clean.

89cherokee2gtmudy

Replaced the IAC. Started fine. Went to drive it few moments ago and idling at 3 grand again! What else will cause it to idle so high. No vacuum or manifold leaks. Also adjusted the TPS per cruisers instructions.