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  #1  
Old November 7th, 2018, 04:19
Black2Door1990 Black2Door1990 is offline
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Erratic Idle

1990 renix 4.0 manual trans
Idle was for a while climbing up to 1700rpm slowly after start up and it would go away once fully warmed up. Now it does not go away. Ive cleaned the iac new tps adjusted, cleaned throtte body, replaced map, new cps, unpluged cts and nothing changes, same with knock sensor... Im almost leaning towards ECU? Any advice on this? Also when I take the vacuum off the map sensor the idle goes down but its rough.
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  #2  
Old November 7th, 2018, 05:38
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cruiser54 cruiser54 is offline
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Re: Erratic Idle

Very unlikely the ECU.

Go to www.cruiser54.com and complete tips 1,3,4, and 5 before doing anything else.
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Old November 8th, 2018, 17:52
uglyrenixxj uglyrenixxj is offline
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Re: Erratic Idle

I just finished effin with the same issue on my 89.
Even tho the tps looked good on the multimeter AND my mt2500, it was bad. I found an oem.mopar unit for 19 bux on ebay. I set the voltages via 2500 instead of with the meter, only because it was an option. Not necessarily a requirement
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Old November 8th, 2018, 17:55
Black2Door1990 Black2Door1990 is offline
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Re: Erratic Idle

Very interesting that it would show the right output yet do something else... Ill try out another tps thank you!
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Old November 8th, 2018, 20:03
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cruiser54 cruiser54 is offline
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Re: Erratic Idle

Hold on. It depends which side of the TPS is being measured. You could measure the trans side and it tests good, but the engine side of the TPS is bad.

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

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.
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. It is covered in detail in Tip 6.

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!Backprobe 2

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.
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Old November 8th, 2018, 23:07
Black2Door1990 Black2Door1990 is offline
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Re: Erratic Idle

My multi-meter only does to the first decimal but Ill try out one of my other tps to see if anything changes. Thanks again dudes!
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