Another high idle thread.. renix

1989 xj, 4.0,aw4, and 117k

I've been chasing down this high idle and slight miss for the longest time it seems. It started out with a leaky injector o ring. I've since replaced all of them, no fix.

Things I've replaced since.
cleaned throttle bottle and iac.
Fuel pump
Plugs,wire,and cap/rotor
Tps replaced and adjusted properly.
Checked and rechecked for vacuum leaks.
Cleaned o2 sensors
Checked and cleaned ground by dipstick.

It idles down to around 900rpm then after about 20 seconds jumps to 1200/1400 idle. Also has a slight miss. Put in drive and it drops down to around 600rpm but miss sounds a little worse.

Im stumped and dont know what else to test.
Someone make me feel stupid with something simple it could be..

Check the +B latch relay. It on the passenger side fender in the row of 4 relays. I think it was the 3rd one back from the front. When it does it wiggle the relay and see if that fixes it. This relay powers the IAC so when the connections are dirty this can happen. If it idles it back down replace the relay. And you say you cleaned the IAC. How did you clean it and did you clean the area in the throttle body that it sits into?

Throttle body cleaner in all every area of throttle body, even the area where the iac sits. Used a cloth to scrub and sprayed it. Looks new. I can unplug the iac and no change in idle. You may be onto something. I'll check the relays after work

Wiggling relays didn't effect anything

Check the MAT Intake Temp sensor resistance at various temps and compare to OEM spec. Mine was a bad MAT sensor.

The miss is not related to the high idle speed issue!!!!

BTW, how did you adjust the TPS, and using which of the connectors?

I'll have to double check the wires but I remember setting it to 17%

Well, I'd do the other two things suggested just because they are knwn issues, cost nothing but a little time to do, and can keep problems at bay in the future.

You may have adjusted your TPS wrong. You set it using the flat connector at 17% of input voltage.

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

let me ask, to be sure of the TPS
on my 4 wire plug i have A B and the other two have no letters.
my 3 wire plug has A B C on it.
am i supposed to go the 3 wire voltage divided by the 4 wire plug voltage? to be the .83 percent?
i can not get rid of my high idle. going right now to clean the cylinder head ground.
i have cleaned and repaired the harness grounds. checked the wires for damage.
much more to my story. but cut to the chase, i have gained a lot but am stuck on high idle.
i thought maybe i am doing the math part wrong. i have been writing down my voltage readings from my Fluke 77 digital multi meter. then do the calculations on my smart phone.

Forget the square 4 wire connector.

Use only the flat 3 wire connector for all testing/adjusting.

http://cruiser54.com/?p=54

cruiser54 said:

Forget the square 4 wire connector.

Use only the flat 3 wire connector for all testing/adjusting.

http://cruiser54.com/?p=54

Click to expand...

Then if you solve the high idle and get odd shift speeds, test and post the square connector voltages, it is also 3 wires, and it can shift point issues. But the square side operates exactly backwards to the flat connector side. The square side talks to the transmission computer only (the TCU). The flat side talks only to the engine computer, the ECU

so the 3 wire, one is ground, and one has voltage. what is the 3rd? and if testing and adjusting on the 3 wire, explain how i am missing what to do

:anon:

Gunter said:

so the 3 wire, one is ground, and one has voltage. what is the 3rd? and if testing and adjusting on the 3 wire, explain how i am missing what to do

Click to expand...

Both sides are independent three wire systems. One is ground, one is apx 5.0 Volts power, the third is the voltage signal from the TPS to the ECU on the flat side.

You should be calibrating using the ground and the return signal line on the flat side for the ECU signal

thank you mike!!

Is this not clear enough?

http://cruiser54.com/?p=54

LOL i misunderstood. i have it now.
my voltage on the flat plug is 4.96V and .381
so 4.96 divided by .381 is 13.01
still no regular idle.
at this point i think one of three avenues. IAC or cpu/transmission module, or still chasing ground wires.
and my voltage goes up when it is running by .17 roughly. is it normal for the voltage to slightly increase once it starts?
and i was so far unable to get to the ground on the back of the head with the tools i have at home. so i have a new ground i made from 6 ga and soldered on ends. from front valve cover bolt to one of the welded in factory nuts for the upper rad support . i sanded all paint and dirt off to have clean connection.

i wanted to mention other improvements and part replacements i have done while working on this problem.
my fuel pump rubber hose came off, so i fixed that and checked my fuel pump pressure. one issue i dont need to worry about.
fuel filter changed.
i had an issue where when hot it didnt want to start again. so replaced the ignition module, and that problem went away.
o2 sensor replaced, old and 240 thousand miles, i think it was money well spent.
block temp sensor. now i have a known good one , and fresh coolant.
the harness that goes to block temp, 02 and knock sensor-- i pulled it out and cleaned it off, all good some heat damage on the insulation but no holes. re wrapped and routed along the stainless steel fuel line and down behind the drivers side engine mount away from the manifold heat and sharp edges.
IAC wires, fished them out of the harness and bypassed the bulkhead connector to be sure that was not my idle problem.
all grounds and their bolts cleaned and repaired as needed.
harness grounds cut out and replaced.
3 relays cleaned and re installed.
the other relay with the 6 wires bolted on, have been cleaned and re installed.
cleaned dist cap and rotor. it helped and i do need to replace in the near future.
it starts up near instantly.
no more no restart when hot.
just saying doing repairs and fixing things, even tho did not fix original complaint, did fix other issues i am happy with. trans shifts good and firm in all 4 gears up and down shifting. i was stuck with 3/4 and high idle only.

thanks for the help everyone, i am almost done with my high idle....almost