Rough Idle

[Lee21490]

So.. ever since i got my comanche it's had a slight miss at idle.

 

The RPM stays solid, But you feel the truck shake

Idles about 750~

Seems to have gotten a lil worse over the last week

 

95 4.0L

No check engine light

New o2 sensor / plugs / wires / cap / rotor / exhaust / just cleaned the throttle body & IAS valve

180k miles

 

 

Any ideas?

[ftpiercecracker1]

thats a pretty stinkin low idle, it might do what its doin because of just that. Its having difficulty staying running at such a low RPM. It might be that your TPS is out of adjustment, Cruiser's got you covered there. :thumbsup:

[Lee21490]

thats a pretty stinkin low idle, it might do what its doin because of just that. Its having difficulty staying running at such a low RPM. It might be that your TPS is out of adjustment, Cruiser's got you covered there. :thumbsup:

 

Cruiser?

 

Is that idle really that low? It seems like one cylinder is missing hard @ idle

[ftpiercecracker1]

750 sounds low to me, but i am basing this off of what mine does with is between 900 and 1100 rpm. How does it drive and run in general?

 

 

 

 

 

 

 

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.

[Lee21490]

750 sounds low to me, but i am basing this off of what mine does with is between 900 and 1100 rpm. How does it drive and run in general?

 

 

 

 

 

 

 

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.

 

 

It runs great, Doesnt really have a problem other then what feels like a cylinder missing at idle.

 

Will that guide even work for me? Its for a Renix 4.0 & i have a 95 HO

[cruiser54]

It runs great, Doesnt really have a problem other then what feels like a cylinder missing at idle.

 

Will that guide even work for me? Its for a Renix 4.0 & i have a 95 HO

 

No. It won't. Make sure all your intake manifold to head bolts are tight.

 

Wiggle each injector plug at idle and see if it changes.

 

750 idle in gear with an auto trans in D or in Neutral?

[Lee21490]

No. It won't. Make sure all your intake manifold to head bolts are tight.

 

Wiggle each injector plug at idle and see if it changes.

 

750 idle in gear with an auto trans in D or in Neutral?

 

In park.

 

Doesnt really change much in drive / park.

 

I'll try that out.

[ComancheKid45]

Check your plug gaps and wire connections, I know you said theyre new but an outta sepc gap caused me near 9 months of headaches over a rough idle ;)

[HOrnbrod]

It runs great, Doesnt really have a problem other then what feels like a cylinder missing at idle.

 

Will that guide even work for me? Its for a Renix 4.0 & i have a 95 HO

 

After a battery disconnect on any 91-95 OBDI HO (if this is what you have) it will idle low and run like crap until it's driven about 100 miles or so, sometimes more. When the battery is disconnected the ECU drops all it's stored memory settings and it must be driven quite awhile until the ECU "re-learns" the settings.

 

Also, if you really have a 95 HO OBDI system, have you checked for fault codes using the ignition key?

[Lee21490]

Check your plug gaps and wire connections, I know you said theyre new but an outta sepc gap caused me near 9 months of headaches over a rough idle ;)

This happened with the old plugs too, And the new ones are pre-gapped.

 

After a battery disconnect on any 91-95 OBDI HO (if this is what you have) it will idle low and run like crap until it's driven about 100 miles or so, sometimes more. When the battery is disconnected the ECU drops all it's stored memory settings and it must be driven quite awhile until the ECU "re-learns" the settings.

 

Also, if you really have a 95 HO OBDI system, have you checked for fault codes using the ignition key?

 

I havent disconnected the battery in a long time.

 

How do i check the fault codes?

[HOrnbrod]

How do i check the fault codes?

 

http://comancheclub.com/topic/28111-reading-obdi-91-and-92-mj-fault-codes/

[Lee21490]

http://comancheclub....mj-fault-codes/

 

I get nothing.

 

Doesnt flash or anything.

[HOrnbrod]

I get nothing.

 

Doesnt flash or anything.

 

I have no idea what system you have. Not a 95 HO OBDI it seems. Is the computer an HO? What does it look like and where is it mounted? And what's the IAS valve you replaced. :dunno:

[Lee21490]

I have no idea what system you have. Not a 95 HO OBDI it seems. Is the computer an HO? What does it look like and where is it mounted? And what's the IAS valve you replaced. :dunno:

 

IAC*

 

Idle Air Control valve

 

 

The engine came out of a 95 Cherokee, So i'm pretty sure thats what it is lol

 

The entire dash / engine / wiring is all from the 95, So I'm assuming its a HO computer.

[HOrnbrod]

IAC*

 

Idle Air Control valve

 

The engine came out of a 95 Cherokee, So i'm pretty sure thats what it is lol

 

The entire dash / engine / wiring is all from the 95, So I'm assuming its a HO computer.

 

You assume it's an HO computer. Where is it mounted and what does it look like? A pic would be helpful. Don't assume anything if you did not do the HO conversion yourself.

[Lee21490]

You assume it's an HO computer. Where is it mounted and what does it look like? A pic would be helpful. Don't assume anything if you did not do the HO conversion yourself.

 

 

Not from mine, But looks exactly the same.

 

Assuming this is what you meant.

 

 

And its mounted in the front left, Next to the air filter

[HOrnbrod]

That's looks correct ECU for the OBDI. Couple of things you can do:

 

1. Unplug the ECU 66-pin connector and check for any recessed, broken, and/or bent pins. Also douch out the connector and receptacle with some electrical contact cleaner before reconnecting.

 

2. There should be a white tag on the case edge. See if you can post all the numbers you find on it so we can determine if it is correct for your vehicle.

 

Also, does the CEL illuminate when you turn on the ignition prior to starting? This is the dash light check and the CEL (as well as the other indicator lights) should all illuminate.

[Lee21490]

That's looks correct ECU for the OBDI. Couple of things you can do:

 

1. Unplug the ECU 66-pin connector and check for any recessed, broken, and/or bent pins. Also douch out the connector and receptacle with some electrical contact cleaner before reconnecting.

 

2. There should be a white tag on the case edge. See if you can post all the numbers you find on it so we can determine if it is correct for your vehicle.

 

Also, does the CEL illuminate when you turn on the ignition prior to starting? This is the dash light check and the CEL (as well as the other indicator lights) should all illuminate.

 

Yea, The Check engine light comes on when i turn on the key.