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Unread 05-13-2013, 11:15 AM   #1
smpotter12
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1988 XJ Cherokee 
 
Join Date: Sep 2012
Location: madera, ca
Posts: 28
High idle on start-up hot days

'88 Jeep Cherokee 4.0 4x4

During the hot months of the year my jeep develops a problem with a high idle upon start up. When I start my jeep the rpm's are up around 2,000 when in neutral/park and about 1,400 when in gear. It will remain like that for a few minutes while I drive and it eventually goes back to normal. During the summer months it has the high idle about 75% of the times that I start it.

I have checked the throttle body and it does not appear to have any build-up that would be getting it stuck open.

What else could cause this kind of problem but only when it is hot outside?

Thanks Gentlemen,
Steve


Last edited by smpotter12; 05-14-2013 at 02:25 PM..
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Unread 05-15-2013, 01:21 PM   #2
smpotter12
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1988 XJ Cherokee 
 
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Location: madera, ca
Posts: 28
No ideas? What vacuums could I check for leaks to possibly fix this problem?
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Unread 05-15-2013, 04:34 PM   #3
bigpapame
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Location: riverside, ca
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I'm glad you posted this thread, Ive just purchased a 88 Cherokee and have had a few intermittent high idles, but mine were after driving for a lil bit. Hope someone has a suggestion.
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Unread 05-16-2013, 10:14 AM   #4
smpotter12
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1988 XJ Cherokee 
 
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Location: madera, ca
Posts: 28
Not sure if you have tried this yet but this guy shows you how to fix one of the causes of the high idle. Might be worth a shot.

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Unread 05-16-2013, 02:22 PM   #5
cruiser54
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1990 MJ Comanche 
 
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Test the TPS per the following instructions. Be sure to use the procedure for the flat 3 wire connector. Also, clean the throttle body and IAC first, along with doing the sensor ground test. Good chance the TPSs have failed.


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
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If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

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