No More Low Idle

[1989 Eliminator]

I will say I had a low idle that was hovering around 400-500 and going through Cruiser54's TPS adjustment and ground refresh, she is idling around 750 now in drive. I already did the engine and chassis ground upgrades but I did not know about the TPS,CTS,IAT, and ECU ground wires that are located in the wire harness by the firewall.

 

Cleaned the throttle body, soldered the five ground wires together (there was orignally a crappy clamp) and adjusted the TPS to the correct spec. Idles like a champ.

 

Before I soldered, I did the ohm's test for the three prong connecter and I had varying resistance. So, after soldering I tried again and that problem was solved. I still have a ~2 ohm reading which is a little high. But nothing to worry about I don't think. When I did the TPS adjustment, my reference voltage was 5.02 V and I adjusted to where the output voltage was .85 V.

 

Cruiser’s Renix Sensor Ground Test
　
This sensor ground circuit affects the CTS, TPS, IAT, MAP, ECU and diagnostic connector grounds. It’s very important and not something to overlook in diagnosing your Renix Jeep as it is common for the harnesses to have poor crimps causing poor grounds. If any or all of the sensors do not have a good ground, the signal the ECU receives from these sensors is inaccurate.
Set your meter to measure Ohms. Be sure the key is in the OFF position. 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 runs parallel to the valve cover and also near the MAP sensor mounted on the firewall. If you have an 87 or 88 with the C101 connector mounted on the firewall above the brake booster, wiggle it, too.
You want to see as close to 0 ohms of resistance as possible. And when wiggling the harnesses/connectors the resistance value should stay low. If there is a variance in the values when wiggling the wires, you have a poor crimp/connection in the wiring harness or a poor ground at the engine dipstick tube stud. On 87 and 88 models, you could have a poor connection at the C101 connector as well.
Revised 06/12/2012

 

 

 

 

Put this together to simplify the TPS testing and adjusting on 87 to 90 Renix Jeeps. There are other procedures out there but half of them are wrong and don't separate out driveability testing from transmission testing like these do. Remember: You must adjust a TPS after replacing it on a Renix Jeep, unlike the later models.

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: 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.
If you see more than 1 ohm of resistance 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. If you have TRANSMISSION 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 11-28-2001

 

[cruiser54]

You just made my day. Thanks for posting this up.

[ftpiercecracker1]

Sticky?   :idea:

[HOrnbrod]

It already is. Look at Cruiser's signature.

[cruiser54]

Sticky?   :idea:

Click on the link in my signature below. I changed the color and text size.

[1989 Eliminator]

You just made my day. Thanks for posting this up.

 

I knew it would! I never knew about those ground wires in the wiring harness.

[cruiser54]

 

You just made my day. Thanks for posting this up.

 

I knew it would! I never knew about those ground wires in the wiring harness.

I found them while putzing around on the 88. 54 to 78 ohms of resistance while wiggling the harness!! Not so good signals to the eCU from some very critical sensors.....

[1989 Eliminator]

Yeah that is exactly what I got. It was kinda hard to solder the wires but I got a good amount on there. Is 750 RPM considered a low idle though?

[cruiser54]

Yeah that is exactly what I got. It was kinda hard to solder the wires but I got a good amount on there. Is 750 RPM considered a low idle though?

Not at all. Ya done good.

[TheDude]

I'm picking up an 89 MJ from a forum member on here. So I'll be devouring that long thread of Renix tips soon enough too! I can't wait!