High Idle and 4x4 light problems

[Nate C]

Hi all,

I'm having problems with my MJ reving real high on start up. I've checked and lubbed the throtle cable and all other connections, I've also sprayed the air intake/butterfly valve with air intake cleaner. No luck as of yet, I can get it to stop if I shut it down then re-start, but that does not work every time.

 

Also I can't get my 4x4 light to shut off, I know the 4wheel drive is not engaged because I don't feel the tugging in tight turns. Whats weird is if I let the engine bog a bit before down shifting the light will turn off for a second or two?? Any advice is appreciated.

[vaquaro]

Initial high rev on start up is normal ,but should drop back quickly . Try the simple stuff first : vacuum leaks - intake/exhaust manifold bolts , TB bolts/gasket , vac lines for cracks or loose fit at connections ( Clamp or replace ). :cheers:

[cruiser54]

After doing the above suggested things, check your TPS on the engine side using these instructions:

 

 

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. 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 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 08-27-2012

[skidoo_j]

The 4x4 light is coming on because the sensor under the purge tank on fire wall is receiving vacuum. Could mean there's a problem at the vacuum valve at the transfer case or at the CAD. The light turns on when the axle is engaged not when the transfer is in 4x4. only real way to see if it's stuck engaged is to jack up front end when running an spin the drivers wheel, if the passenger side spins the actuator is holding the front axle locked.

 

It will not cause any problems, they did away with the cad and put a solid axle on the passenger side in later models, often upgrade by those of us with CAD.

 

Your extreme idle could also be a stuck IAC.

 

 

 

 

 

http://www.lunghd.com/Tech_Articles/Eng ... ostics.htm

[Nate C]

After doing the above suggested things, check your TPS on the engine side using these instructions:

 

 

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. 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 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 08-27-2012

 

 

Wow, that will keep me busy for a while, thanks the detailed writeup!

[Nate C]

The 4x4 light is coming on because the sensor under the purge tank on fire wall is receiving vacuum. Could mean there's a problem at the vacuum valve at the transfer case or at the CAD. The light turns on when the axle is engaged not when the transfer is in 4x4. only real way to see if it's stuck engaged is to jack up front end when running an spin the drivers wheel, if the passenger side spins the actuator is holding the front axle locked.

 

It will not cause any problems, they did away with the cad and put a solid axle on the passenger side in later models, often upgrade by those of us with CAD.

 

Your extreme idle could also be a stuck IAC.

 

Good tips thanks, I checked the connections at the T-case then traced the vacuum lines up

to their connection point. Everything appeared to be connected properly. Help me out with those abbreviations, what is the CAD and IAC? I thought there was an acronym decoder on this site somewhere.

 

 

 

http://www.lunghd.com/Tech_Articles/Eng ... ostics.htm

[skidoo_j]

The 4x4 light is coming on because the sensor under the purge tank on fire wall is receiving vacuum. Could mean there's a problem at the vacuum valve at the transfer case or at the CAD. The light turns on when the axle is engaged not when the transfer is in 4x4. only real way to see if it's stuck engaged is to jack up front end when running an spin the drivers wheel, if the passenger side spins the actuator is holding the front axle locked.

 

It will not cause any problems, they did away with the cad and put a solid axle on the passenger side in later models, often upgrade by those of us with CAD.

 

Your extreme idle could also be a stuck IAC.

 

 

 

 

 

http://www.lunghd.com/Tech_Articles/Eng ... ostics.htm

Good tips thanks, I checked the connections at the T-case then traced the vacuum lines up

to their connection point. Everything appeared to be connected properly. Help me out with those abbreviations, what is the CAD and IAC? I thought there was an acronym decoder on this site somewhere.

 

IAC Idle Air Controller It's on your throttle body. Its controlled by your ecu and moves a pintle in and out to control air flow at idle. During start it opens wide and is supposed to then close to control your idle 500-700 rpm.

 

 

CAD central axle disconnect. It's a vacuum actuated fork that moves a shift collar connecting your inner an outer axle on the passenger side. It's controlled by a valve on the back of the transfer case. When in 4x4 it allows vacuum to pull the fork into the locked position, the vacuum then continues up to the switch that controls the dash light. The switch on mine was a blue round thing under the purge tank near the fire wall. It is a switch to ground.

 

First test the switch by disconnecting the vacuum to the switch, if the light goes out then the light switch is good and your problem is the actuator at the axle or the switch at the back of the transfer case.

[Pete M]

do this:

viewtopic.php?f=9&t=18415

and then just ignore the 4x4 light. :D

 

 

also, here's the acronym chart:

viewtopic.php?f=9&t=12815

 

:thumbsup: