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Unread 06-14-2012, 08:34 PM   #1
electricman
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Idle Issue

I have a 1989 manual XJ, and every time I shift into neutral, the idle changes. Sometimes, it will idle really high while other times, it will act completely normal. Even in gear, sometimes it will begin to accelerate without my foot touching the gas. Unfortunately, I can't give the rpm because I don't have a tachometer. Does anyone have any comments?

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Unread 06-15-2012, 06:18 AM   #2
cruiser54
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Sounds like you may have a bad Throttle Position Sensor. Got a voltmeter and know how to use it?
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Unread 06-17-2012, 10:55 AM   #3
electricman
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Yes. Where is the sensor? I have also been having some electrical issues lately, so could it be the wiring?
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Unread 06-17-2012, 11:07 AM   #4
Armycherokee
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It is on the throttle body the plug will be facing the firewall
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Unread 06-17-2012, 12:37 PM   #5
cruiser54
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Quote:
Originally Posted by electricman View Post
Yes. Where is the sensor? I have also been having some electrical issues lately, so could it be the wiring?
Yes, it could very well be the wiring. The REnix Jeeps had grounding issues. I'm attaching my TPS instructions. But, take note of the IMPORTANT note in the beginning. That's a simple sensor ground test. Do it first. Your TPS is located on the front of your throttle bode body closest to the driver's fender.


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 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.
FOR AUTOMATIC TRANSMISSION RELATED 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.
Revised 05-28-2012
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Unread 06-19-2012, 05:22 PM   #6
electricman
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Okay, I probed all of the connections. The ground connection was fine even when wiggled. The voltage of the sensor was slightly lower than expected, however. It measured .99 volts while my reference was 6.48 volts.

While I was in there though, I looked at the TB valve and found that it was relatively clean, but it did have a little carbon buildup around the edges. I also noticed a bit of oil where the air tube connects to TB. Is that normal?
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Unread 06-19-2012, 05:35 PM   #7
cruiser54
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Reference voltage should never be over 5 volts. Maybe use a different meter.

Normal to have some crap in the TB. Clean it out with oxygen sensor safe cleaner.
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Unread 06-21-2012, 07:46 PM   #8
electricman
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Thanks for the advice on the multimeter. This time I used an older analog one: It measured about 4.8V for reference, .75V for sensor, so its still a bit lower than 17 percent.

I also measured across terminals on the car battery in case that could effect the measurement. It measured 12.1V.
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