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Renix Cherokee Idling Issue

ssand746

NAXJA Forum User
Location
WI
Hello all,
I am having an issue with my 1989 Jeep Cherokee Limited 4.0L. It has a high idle at start up, going up to 2500 to 3000 rpm and it does't want to come down. Background info is that I have read through the forums and have seen several posts with similar issues and I believe I have tried all the fixes already. I refreshed all the grounds, and added the extra 2 ground cables that is mentioned in the instructions.I have thoroughly cleaned the throttle body. I have checked for vacuum leaks using starting fluid throughout the engine compartment, especially near the intake with no findings. I replaced the MAP sensor and IAC valve. I replaced the TPS even though it checked good based on voltage readings and the ground tested almost no resistance. I have probably done more, this is just what I can think of as of right now. The thing is, with the old or new TPS, once the engine is started and idling high, if you unplug the 3 wire plug from the TPS (engine side), it will idle down to 7-800 rpm. Then if you plug it back in it stays idling fine until the next startup. My question is what could be causing this at this point? Should I just leave it unplugged? Thanks for any help!!!
 
Not to hijack this thread, but I have a similar issue, but it is intermittent. On some starts mine will idle high (2,000+ RPM) and won't come down. If I shut it off and re-start it, it will then (most of the time) idle normally. ASD relay as well?
 
I had that problem years ago, and it turned out to be the IAT Intake Air temp sensor that was bad (or totally fouled).

If disconnecting the TPS fixes it, it is not a vacuum leak or IAC or IMHO an ASD relay issue, it is a Renix ECU algorithm issue where it is miss using bad data from the IAT relay or the O2 sensor maybe????

If disconnecting the TPS did not fix it, I would agree the ASD relay might be at fault, But I have never had a bad one, yet.

One other thing I would check is the TPS harness side connector pins and wiring to the ECU, if they are not making solid connections, or the wiring is damaged I could sure see that causing the issue too. Keep in mind the Renix TPS has two independent grounds, and two sides to the sensor, so be sure you are calibrating and testing the 3 pin flat connector and not the square connector for this problem.
 
Not to hijack this thread, but I have a similar issue, but it is intermittent. On some starts mine will idle high (2,000+ RPM) and won't come down. If I shut it off and re-start it, it will then (most of the time) idle normally. ASD relay as well?

yes
 

I am no expert on the Renix ASD relay issues, but once the jeep is started, if the ECU, sensors and IAC valve are working properly, why can't the IAC reset the idle speed to 750 adjusting the ? How would an ASD relay issue stop the IAC from corrected the high idle?
 
Automatic Shutdown Relay.

It takes a signal from the ECU and holds the power on long enough for the ECU to RESET the IAC to the correct position for start up when you turn off the key.

If this does not happen on shutdown, when you start, the idle goes way high. After a few seconds, the ECU normally will correct and walk the IAC back to an idle position. I have seen multiple occasions where that did not happen well. That may be caused by a bad TPS or ??? who knows.

The nice thing is that the relays are a standard Bosch type cube relay, and to troubleshoot, you can swap with one of the other relays in the row temporarily.
 
I have always wondered if that is really true, for this reason.

The IAC setting should depend on coolant temperature and intake air temperature and even MAP sensor data when the tries to start or when it is idling, hot or cold (with the O2 sensor trimming it).

Once the rig starts the ASD relay has nothing to do with IAC/ECU establishing the proper idle at 750 rpm. Even if the rig starts at say 2000 rpm, it IAC valve should in seconds correct the idle. If it is not, the problem can not be the ASD relay.

Also I would think (but could be wrong) that when the Ign switch is cycled to run that ECU should look at engine and air temps and adjust the IAC valve 1-2 seconds before cranking, if one waits a few seconds.

The part that bothers me is a restart can be hot or cold, so how does the ECU know where to set the IAC valve for a restart when the ASD relay gives it time and power to reset.

Why would it even need to be reset if the rig is turned off and turned back on 5 minutes later????

I may dig out the Renix guide book and read up this as I suspect there is more to it than just an ASD relay resetting it for an unknown future temp condition restart.

Perhaps it sets the IAC to match an ECU fuel injection rate table for Open loop starts that ignores the engine and air temps??? But I know that when I had a bad IAT Intake Air temp sensor the ASD relay had nothing to do with my cold engine non starts and hot engine high idles. It was a bad IAT sensor. So the ECU must be using that data for restarts!!!
 
Good question, I guess it is called an ASD relay by 1996 OBD-II ????

I have never had an issue with that one, ever. But others talk about the ASD a lot. Was it renamed I wonder?



Are you guys talking about the Power Latch Relay?

3rd one back in the gang of four relays?

https://i.imgur.com/AfN4IwL.jpg
 
Hello all,
I am having an issue with my 1989 Jeep Cherokee Limited 4.0L. It has a high idle at start up, going up to 2500 to 3000 rpm and it does't want to come down. Background info is that I have read through the forums and have seen several posts with similar issues and I believe I have tried all the fixes already. I refreshed all the grounds, and added the extra 2 ground cables that is mentioned in the instructions.I have thoroughly cleaned the throttle body. I have checked for vacuum leaks using starting fluid throughout the engine compartment, especially near the intake with no findings. I replaced the MAP sensor and IAC valve. I replaced the TPS even though it checked good based on voltage readings and the ground tested almost no resistance. I have probably done more, this is just what I can think of as of right now. The thing is, with the old or new TPS, once the engine is started and idling high, if you unplug the 3 wire plug from the TPS (engine side), it will idle down to 7-800 rpm. Then if you plug it back in it stays idling fine until the next startup. My question is what could be causing this at this point? Should I just leave it unplugged? Thanks for any help!!!

Mine does the same thing. But not every time I start it. If I tap on the IAC with a tool after it starts high RPM the pintal moves back in and then idles fine. Its a new IAC too. Replaced it because the old one did the same thing.
 
Have not done tip #5.

Because all my wire looms need replacing, brittle, due to heat soaked, will be a great time for tip#5.

Will see how many of my issues go away after tip #5.

Occasional high RPM at cold and warm start. Tap on IAC starts normal.
Occasional high idle after driving a few miles.
Long crank time when cold. Unless parking on a slight decline, starts 1st or 2nd crank (new fuel pump), means nothing.
Cold start, idle hunting for first 30 seconds or so.

I do have slight oil seepage between head and block. No oil in Coolant, no coolant in oil. It maybe a source of a vacuum leak there. Could be the cause of my cold start idle hunting.
 
I had that issue with idling/starting as well and turns out it was both an IAC and a TPS issue. TPS connector is fully worn out but patched it to work ok after discovering a wire break and with the new IAC the idle no longer starts high or stays high. I am rebuilding all 3-pin connectors with weatherpacks I ordered from Amazon.
 
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