Guess what?? another renix low rough idle.

[Ecomike]

Disconect the O2 sensor. Does the idle still wander?

If Yes= then it is not the closed loop or O2 sensor problem. Perhaps a bad Injector connector. I have had that problem with 2 connectors.

No= Check the Air Intake temp sensor, I had one cause wander and a high idle as it failed. Liked to never figured that one out. Also I connected the O2 sensor connector backwards once and it caused low idle and wander in the 200-350 rpm range. IIRC connecting the TPS 3 prong connector backwards does that too. My connectors had broken plastic and it is possible to connect them backwards.

 

[Ecomike]

wouldnt it just cause a slower drop into closed loop?

not sure how it could affect the idle

Movement of a busted but partially connected wire or connection can cause swings in the voltage signal and thus a wandering idle response as the computer hunts with bad data inputs.

3 Ohms is too high a resistance for the O2 sensor ground wire!!!! It must tested with the O2 sensor disconnected, power off.

 

[Ecomike]

did a little sleuthing and found out the far right relay is infact the ac relay and the far left is the 02 heater relay.

so i decided i would test the wires again with the truck running.

orange wire 9.52 volts grounding to the connector. which is strange. what could cause it to get that low voltage, i switched relays around and made no difference.

the relay connector is getting 12v.

the ground wire read at 3ohms i think.

Relay contacts could be fouled and dirty. Should read 14 volts disconnected from the O2 sensor. Might be seeing a voltage drop from the O2 heater load on the entire circuit. IIRC the heater is an 8 ohm resistor.

 

[AKghandi]

the manifold temp sensor is one I have not changed, I cannot find one that works, they all have the wrong connector. however problem remains with it hooked up or not.

I hear its the same as the coolant temp sensor so I may just go cut a connector off a parts rig and run a new coolant temp sensor.

I say the ground was at 3 ohms "I think" because I could only get a reading at the 2k ohm setting. it came out as 0.003. not 100% on how to read that. I know I have checked and double checked every ground.

with the O2 unhooked it does still wander, as it does with every other sensor unplugged minus the map and crank sensor.

I have switched the map, and even switched back to the original, and one off my other truck.. no change.

there is a change when each injector is unplugged. don't know if they would be the issue.

 

[cruiser54]

Pay attention to Mike's suggestions.

Quit changing stuff willy-nilly.

The IAT can be tested with a meter quite easily.

 

[truckeejeeper]

x2 on the IAT, as Ecomike sez. I just cleaned mine w/ carb cleaner and it totally fixed my rough acceleration.

 

[Royal Nonesuch]

the manifold temp sensor is one I have not changed, I cannot find one that works, they all have the wrong connector. however problem remains with it hooked up or not.

I hear its the same as the coolant temp sensor so I may just go cut a connector off a parts rig and run a new coolant temp sensor.

The MAT/IAT looks like this:

The CTS looks like this:

They are physically very similar, but as you can see the MAT is designed for airflow and I don't think you could really interchange them. Hell, I don't have them on hand but I think the size/threading is different anyway. I've heard that said before, and according to the old LungHD sensor testing charts they both have the same ohm resistance at different temperatures, so that might be why people think that?

The IAT can be tested with a meter quite easily.

This is a much better bet. I pulled mine out and it was absolutely filthy. I cleaned it with throttle body cleaner and tested it with a multimeter. It was perfectly in range of the numbers in that chart at operating temp. To be sure, I used an IR temp gun to measure the intake manifold temp through the mounting hole. I also tested a few junkyard spares while I was at it and they were all within range as well, so I don't think they go bad too easily. Clean + test yours and grab spares at the JY when you see them - they're almost impossible to find new for 1987-1991.

 

[Ecomike]

The response time of CTS would not be fast enough to works as an IAT/MAT sensor.

There is an old, 4 years or so, thread here with the part number of a replacement Air intake sensor for the Renix jeeps that just needs the connector end swapped with $2 connector off ebay, using the old 1980's GM Weatherpack series connectors.

Nice photos Royal, and hello.

 

[Ecomike]

the manifold temp sensor is one I have not changed, I cannot find one that works, they all have the wrong connector. however problem remains with it hooked up or not.

I hear its the same as the coolant temp sensor so I may just go cut a connector off a parts rig and run a new coolant temp sensor.

I say the ground was at 3 ohms "I think" because I could only get a reading at the 2k ohm setting. it came out as 0.003. not 100% on how to read that. I know I have checked and double checked every ground.

with the O2 unhooked it does still wander, as it does with every other sensor unplugged minus the map and crank sensor.

I have switched the map, and even switched back to the original, and one off my other truck.. no change.

there is a change when each injector is unplugged. don't know if they would be the issue.

That sounds like an air or fuel leak. Has the fuel pressure regulator vacuum line connection been checked for a gasoline odor, a sign of gas leaking into the engine, by passing the injectors (bad FPR diaphragm).

Injector oring's leaking air, injector dirty, not sealing shut, leaking fuel, just one would do it.

 

[AKghandi]

That sounds like an air or fuel leak. Has the fuel pressure regulator vacuum line connection been checked for a gasoline odor, a sign of gas leaking into the engine, by passing the injectors (bad FPR diaphragm).

Injector oring's leaking air, injector dirty, not sealing shut, leaking fuel, just one would do it.

Fpr is good so is the vac line. new injector o rings switching injectors with other truck made no difference.
Pressure is correct and bleed down within spec.

Today i measured the MAT/IAT. Read almost exactly where is should be according to lunghd. Took it out was kinda dirty so I cleaned it. No change to idle feels like theres a bit more power but that may just be a mental thing.

Put a stock oriface tube back on. Idle is lower as i expected.

Also i would like to say that replacing all these parts is fine with me. Ill switch the engine to get it right(already have one on a stand) Its not about money for me its about peace of mind. didnt buy a jeep to save money. Where i live a break down could be fatal in winter time.
Thats why every sensor i have replaced good or bad is in a box in the back. There is method to my madness

I also remembered something pretty important. I read a thread where someone welded on their jeep and it killed the ecm even with one of the battery cables diconnected. Well i had to weld my throttle pedal back on and i wonder if it caused an issue with the ecm. It was one of the first repairs i did way back when it was running like absolute trash. So i cant be sure if it had this issue back then.

Going to grab a new ecm and see if it changes if not ill return it.

 

[AKghandi]

https://youtu.be/Pfh2NAkHG2M

 

[AKghandi]

Was reading through the fam and came across a spark plug p# rfn14ly, noticed it looks quite different than the autolites i have in the truck now. So i went and got some stock#82. Gapped and installed them.

Its idling at 850!!! Still wandering but the idle is actually too high which im guessing is to do with the air bleed screw i adjusted.

Not sure the science or engineering behind this but i can only assume the longer electrode gets further into the cylinder and give a better more complete burn.

 

[AKghandi]

So it is not completely fixed, the idle now varies between 750-850 then it will sometimes decide to be at 300-400...

only thing I can think is the ECM at this point. My reasoning for this is the idle is computer controlled. the IAC works and moves if I drown the truck with carb cleaner I can watch the IAC move. everything is clean. everything is adjusted properly. the IAC is pretty much seated at idle.

The idle is computer controlled, therefore with a functioning IAC and a functioning CPS to give RPM signal, it must be a computer issue.

Unless there is some unknown mechanical issue that would cause an engine to idle low but still perform well.

My other thought is that the timing is also computer controlled. the knock sensor is not hooked up. so if the timing system was failed in some way it could retard the timing and bring the idle down.

this is less likely as the truck does perform pretty well. itll get to 60 pretty quick even with stock gears and 70lbs of 33s at each corner

 

[87manche]

so you changed the IAC or no?

just because it moves doesn't mean that it's responding correctly. Unfortunately the only way to properly test it is with a DRB II.
I grab them at junkyards so I have extras to try. I hate parts shotgunning, but the IAC is just one of those things that you can't test well as a DIY mechanic.

One day I will own a DRB II

 

[AKghandi]

i have switched the iac twice. thank god for life time warrantys. also put a used one in. no difference.

 

[Ecomike]

You changed the plugs and got a huge change right? Tried new plug wires, cap and rotor yet?

 

[AKghandi]

yes. cap rotor and wires are new.

even cleaned up the distributor.

 

[Royal Nonesuch]

There is an old, 4 years or so, thread here with the part number of a replacement Air intake sensor for the Renix jeeps that just needs the connector end swapped with $2 connector off ebay, using the old 1980's GM Weatherpack series connectors.

I have this one bookmarked from awhile ago when I thought I might need to find a new one - http://www.injector.com/cart/pc/viewPrd.asp?idproduct=65&idcategory=12. IIRC it's the right sensor, you just might have to do some connector splicing. I never ordered one because I think that site has a minimum order $$ amount and the shipping was also prohibitively expensive. Might come in useful for someone in the future though.

Nice photos Royal, and hello.

Hey and thanks - not my photos, just rehosted, but I like to try to make things easier with visual aids.

AKghandi - I've mentioned this in other threads but I fought a low idle for a long time until emissions testing finally made me figure it out... My injector pigtails were crossed over on the 3-4 and 5-6 injectors. I had screwed them up somewhere in the past. Unlikely in most cases, but easy to check - pull back the rubber boot at each injector and check to see if the wire colors match the following:

Cylinder 1-light blue
Cylinder 2-light green
Cylinder 3-tan
Cylinder 4-yellow
Cylinder 5-white
Cylinder 6-brown

I corrected my error and it ran really weirdly at first until I disconnected the battery leads and touched 'em together like you'd do for a newer OBDI jeep, and it has idled perfectly at 750 since then. You might also want to bite the bullet and go eliminate the C101 connnector as cruiser instructs in his tips. Maybe replace the distributor coil and clean where it connects? They're like $15 IIRC.

 

[AKghandi]

thanks royal. i will look into that.

I dont have a c101.

ICM and coil are new. those actually did fail. left me on the trail, then the side of the highway.. then a parking lot.. and so on. no problems since

 

[AKghandi]

just went out and check my injector wires.

5 and 6 were switched. 3 and 4 were fine. 1 and 2 are a little suspect as they are very similar colors. ill have another look tomorrow some time.

i reset the ecm and it didnt seem to change much aside from it reving a bit better.

in other news I got a new intake manifold egr tube and vacuum harness. going to put my egr back in working order.might help with my mpgs so its worth it. may also help with my idle/mis issues

also got a handful of those spring washers as i am missing a few on my exhaust manifold

speaking of mpgs, those plugs netted me about 2 mpg. going to run through another tank to be sure but its an improvement for sure. trip shows 153 and i still a little gas left. thats non corrected so figure add about 17%. previously most i would get from 16 gallons was about 130. non corrected.