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over reving after heating up

Offroad Clown

NAXJA Forum User
Location
Peoria
hey guys I have been having issues with my 89 Jeep Cherokee Jumping to about 3 thousand Rpm after the engine has been running for a lil while and been shut off and restarted i have been told to clean the ground wires that bolt to the dip stick for the oil. I have cleaned them. and i have changed the relays on the passenger side and it still tends to jump to 3 thousand after restarting after being warmed up and i cant figure it out at all any leads that can possibly help me please let me know?
 
Your TPS is probably taking a dump on you.

Check it using the flat 3 wire connector:


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 body and 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
 
The engine will only rev as high as it can get air for. You most likely have a leaky intake manifold gasket or a bad/loose throttle body/gasket.
 
Bad TPS. Mine checked out ok per Cruiser's tips, BUT everything still pointed to it(I didn't have an analog multimeter at the time). Replaced it (NAPA) and
not a problem since then.

Cruiser54's guidance made me do it:roflmao:
 
Intake vacuum leak is number one on the list, TPS is number two and number 3, if it comes and goes just switching the engine on and off, is the MAT, IAT air temp sensor. I had one rev up to 3000 rpm some times at idle, and not others, mostly when it was hot, hard to start on cold mornings, and the idle would go back to normal by disconecting the TPS or restarting it. It was the air intake temp sensor that was bad.
 
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