Renix Low idle issues (not your average bear)

[Ecomike]

The OP here has not yet solved his problem, and it gets way too confusing to troubleshoot more than tough problem in the same thread at the same time, especially when the problem seems to be a real challenge. At this point it would be best to start a new thread, and give us a complete history of your problem, what you tried, the order you tried it in, DETAILS, not Just an "I tried everything", but supply us test data numbers, parts tried were new or used, known good parts, why they were known good parts, what the problem is, does the problem come and go randomly or ???? Have you actually tested the sensors per the FSM, what results did you get, and so on. What other recent problems have you had, and how did you fix them?....

Have you read the "RenX Files" thread yet?

 

[8Mud]

I eventually cured my 500 RPM idle, it was a collection of faults that added up. I idle at 650 now, close enough for me.

Just for giggles, try a jumper with a couple of alligator clips from the TPS ground, to chassis ground and see what happens. I stripped a little insulation off of the TPS wires and ran them over the intake rubber elbow, been that way for 7-8 years now, makes TPS tests really easy.

Clean the connector well, I use a quality contact cleaner and one of those tiny toothbrushes for cleaning between your teeth. WD 40 on my connector was my first great discovery when I first began troubleshooting mine after acquiring it used, many years ago. WD 40 is a poor conductor.

I sprayed my IAC with brake cleaner, into the gap between the piston and the case. Then let a little synthetic motor oil run back there as a lubricant. I once dissembled an IAC and the grease behind the piston was almost a solid, with carbon and grit mixed in.

I also screwed open my throttle plate adjuster a tiny bit and then readjusted the TPS.

You need a good battery for the IAC to function well, it seems it needs every bit of voltage it can get. One of the first signs of a failing battery can be a sluggish IAC.

Mike covered most all of this stuff in the Renix files, something I reread periodically, a bunch of good info in there.

I think the reason for initial adjustment of the IAC pintle is to make sure it isn't damaged during assembly. Sometimes they come from the factory with the pintal way out and when screwing the IAC screws back into the throttle body the pintle/piston shaft gets stripped or bent.

 

[Ecomike]

8MUD,

Nice to see you are still alive and kicking, LOL! You got me to thinking, on the IAC, it is operating under a hot vacuum!!!! I ran into this issue on my diesel engine once, oil lubed Leather Diaphragm drying out under heavy diesel engine vacuum, naturally aspirated differential pressure gadget!!!), and discovered that a vacuum pump oil, thin, and very stable under a vacuum and heat, seems to last a lot longer as a lube under those conditions. I just happened to have a bunch of that vacuum pump oil. It work far better than I expected, 5 years so far and eliminated a 4 times a year lube job!

Next time I have an IAC pulled it will get vacuum pump oil!!!!!

 

[8Mud]

8MUD,

Nice to see you are still alive and kicking, LOL! You got me to thinking, on the IAC, it is operating under a hot vacuum!!!! I ran into this issue on my diesel engine once, oil lubed Leather Diaphragm drying out under heavy diesel engine vacuum, naturally aspirated differential pressure gadget!!!), and discovered that a vacuum pump oil, thin, and very stable under a vacuum and heat, seems to last a lot longer as a lube under those conditions. I just happened to have a bunch of that vacuum pump oil. It work far better than I expected, 5 years so far and eliminated a 4 times a year lube job!

Next time I have an IAC pulled it will get vacuum pump oil!!!!!

Worth a shot, I have a bottle of vacuum pump oil on the shelf, though it is likely twenty years old by now. It seems to adhere really well. I've gotten in the habit of cleaning the IAC twice a year, spring and fall. It beats trying to clean it in the middle of the winter (20 degrees out) when the IAC gets sluggish and the motor stalls. I spray some solvent in the gap between the piston and the housing, blow it out and let a little oil flow in there. There is a little electric motor in there, a mild solvent would likely be safest. The IAC is not something I'd want to use carb cleaner or acetone on.

Yes I'm still alive and kicking, old as dirt .

 

[Muad'Dib]

Finally got the Jeep back... while it was gone i purchased an ECU from the Junk yard. Swapped in the ECU and the first start the IDLE was still the same.. but after a couple of starts the IAC pintle did not close all the way like before. So now when i start the engine, the RPM's go up to about 3000 and then drops down to 750ish.


So to make a long story short my ECU was bad.

 

[2stix]

does the idle stay up at 750 rpm even after warm up? i am fighting a similar problem and get a good 750 rpm idle at start now, but drops after a minute or two. way down to 200/300 rpm. i have tried a spare ECU i took from a parts jeep with not change, but i didnt leave it in for that many re starts. maybe i should re try it.

glad you got yours figured out. i KNOW the frustration. congrats man.

 

[Ecomike]

Finally got the Jeep back... while it was gone i purchased an ECU from the Junk yard. Swapped in the ECU and the first start the IDLE was still the same.. but after a couple of starts the IAC pintle did not close all the way like before. So now when i start the engine, the RPM's go up to about 3000 and then drops down to 750ish.


So to make a long story short my ECU was bad.

I have seen that sort of change after 3-4 restarts, with out changing the ECU. I still believe Renix ECUs have a some sort of history table they keep in volatile memory, that is cleared after a battery disconnect, and re-written in part after each start, but no else believes this me besides me.

Perhaps it is the E-Renix Gremlins with the memory, and not the ECU. LOL!

 

[2stix]

i think i read in the FSM that the ECU stores certain codes while a DR2 is connected, but not sure if it was the ECU that stores them or the tester itself. from what i understood, it was the ECU. so i think you have a valid point and are not alone. what i would like to know is if the there is a fault and the ECU goes into a mode to overcome that fault, how does it know to when to return to its normal operation once the fault cause is fixed? from what i understand, it does not have a self diagnostic schedule. does that make sense?

 

[cruiser54]

3000 on start-up is high. Still doing that?

 

[Ecomike]

i think i read in the FSM that the ECU stores certain codes while a DR2 is connected, but not sure if it was the ECU that stores them or the tester itself. from what i understood, it was the ECU. so i think you have a valid point and are not alone. what i would like to know is if the there is a fault and the ECU goes into a mode to overcome that fault, how does it know to when to return to its normal operation once the fault cause is fixed? from what i understand, it does not have a self diagnostic schedule. does that make sense?

It will lock out a bad sensor reading and default to open loop mode if it can not run in closed loop mode. Bad O2 sensor readings would cause it to run open loop. In open loop it uses data tables instead of live O2 sensor data to set timing and fuel rates. I never heard anyone say that it sets diagnostic or trouble codes of any kind at all. But the Scanners that work on renix should be able to recognize bad sensor data and open loop versus closed loop operation, with out any codes. I think it starts at a no fault status each time Renix is restarted.

I have suspected for a long time that it stores min and max sensor data from prior operating runs.

 

[Ecomike]

3000 on start-up is high. Still doing that?

X2, on that. Neither of mine spike over 1000 rpm on start up.

 

[2stix]

It will lock out a bad sensor reading and default to open loop mode if it can not run in closed loop mode. Bad O2 sensor readings would cause it to run open loop. In open loop it uses data tables instead of live O2 sensor data to set timing and fuel rates. I never heard anyone say that it sets diagnostic or trouble codes of any kind at all. But the Scanners that work on renix should be able to recognize bad sensor data and open loop versus closed loop operation, with out any codes. I think it starts at a no fault status each time Renix is restarted.

I have suspected for a long time that it stores min and max sensor data from prior operating runs.

that is pretty much what i figured.
my 89 seems to start each time in its fault free mode. then as the rpms lower from it's initial 1500 rpm and reaches it's operating rpm (750) it will only stay there for a second or two. then i am guessing the ECU is finding a sensor fault and lowing the idle in 1 second intervals. till it reaches it's lowest possible rpm before dieing. barely wants to idle. it runs good at 750 rpm, but i can not get it to stay there. at the moment i am trying my spare ECU hoping i would have the same luck as the OP. but no luck yet. i was hoping that with the new ECU, it should not have any fault codes stored just in case they do store them somehow.

 

[Ecomike]

If they stored a bad code, disconnecting the battery for a few minutes would clear it. Sounds like a bad sensor or bad wiring-connector problem.

 

[2stix]

yep, probably so.