can a bad o2 cause rough idle, but no other symptoms?

I had a continuous rough idle one, ran out of ideas. Ran the compression test, and found an inter cylinder head gasket leak between 2 cylinders. Rare, but does happen. Ran great at higher rpms. Only sign of head gasket leak was rough idle with this one. Oil and coolant were all fine. I doubt it is your problem. You said yours was random, which sounds like loose wires, or bad sensors like TPS with a bad idle spot on the sensor.
 
stephenspann27 said:
I haven't touched the CPS... if the heater on the o2 sensor is reading open.. it has to be that right? Just has to...
Click to expand...

If the random rough idle goes away with the O2 sensor disconnected, then yes, otherwise no. It could be two problems!!!!! And you might have found just one of them!
 
Ecomike said:
I had a continuous rough idle one, ran out of ideas. Ran the compression test, and found an inter cylinder head gasket leak between 2 cylinders. Rare, but does happen. Ran great at higher rpms. Only sign of head gasket leak was rough idle with this one. Oil and coolant were all fine. I doubt it is your problem. You said yours was random, which sounds like loose wires, or bad sensors like TPS with a bad idle spot on the sensor.
Click to expand...

I had my old head off once, to replace the lifters, then I later replaced the head with a reman, during those swaps there is no changed the idle,I think I can rule out the head gasket. As far as the TPS goes.. I've even swapped on the throttle body off my parts jeep with the other parts jeep TPS still on it.. no change.. so TPS can be ruled out...


Why aren't you willing to admit the heating element being bad in the o2 is causing the bad idle (I'm trying to sleep tonight and you are keeping me from putting this problem to bed) :-)
 
stephenspann27 said:
I had my old head off once, to replace the lifters, then I later replaced the head with a reman, during those swaps there is no changed the idle,I think I can rule out the head gasket. As far as the TPS goes.. I've even swapped on the throttle body off my parts jeep with the other parts jeep TPS still on it.. no change.. so TPS can be ruled out...


Why aren't you willing to admit the heating element being bad in the o2 is causing the bad idle (I'm trying to sleep tonight and you are keeping me from putting this problem to bed) :-)
Click to expand...


Like I said, in its present state, it can cause a random rough idle, but only if it is connected to the wiring harness. You have probably found one of the causes. I found 5 total different causes of my low MPGs on the 87 when I bought it, LOL.

Go get some sleep and pretend that is THE solution, and O2 sensor, LOL.
 
stephenspann27 said:
I had my old head off once, to replace the lifters, then I later replaced the head with a reman, during those swaps there is no changed the idle,I think I can rule out the head gasket. As far as the TPS goes.. I've even swapped on the throttle body off my parts jeep with the other parts jeep TPS still on it.. no change.. so TPS can be ruled out...


Why aren't you willing to admit the heating element being bad in the o2 is causing the bad idle (I'm trying to sleep tonight and you are keeping me from putting this problem to bed) :-)
Click to expand...

But you might want to sleep on your earlier statement too:

"However, I completely unplugged the o2 and drove around.. and it ran exactly the same as when its plugged in.. I plugged it in while it was running and there was no change in idle"

I take it this means the idle was rough with the O2 sensor not connected, and with it connected?

What spark plugs are you running?
 
It's an easy test to see if the o2 heater is working without ohming wires. Put an amp probe in the heater circuit fuse socket. Checks the element, power and ground all at once.

It doesn't really sound like an O2 problem to me though. Hard to say without hearing the idle. Once again access to a scan tool to show fuel trims and other live data would put the problem to bed quick.
 
JJacobs said:
It's an easy test to see if the o2 heater is working without ohming wires. Put an amp probe in the heater circuit fuse socket. Checks the element, power and ground all at once.

It doesn't really sound like an O2 problem to me though. Hard to say without hearing the idle. Once again access to a scan tool to show fuel trims and other live data would put the problem to bed quick.
Click to expand...

You do know it is an 87 Renix? He already said the heater element in the O2 sensor is open.
 
The reason I think it ran the same without the o2 plugged in is because the o2 is not getting "warm" and the ECU uses a default value in that case.. so whether its plugged in or not.. it will run the same at idle.. when the heating element is bad.

When i drove it around I drove around my subdivision.. so i didn't get over 20mph..

I'm running some NGK V power plugs..
 
Ecomike said:
You do know it is an 87 Renix? He already said the heater element in the O2 sensor is open.
Click to expand...

Yeah, I saw it's an 87, what's your point? An open heater element doesn't automatically equal rough running. The alternative test for an open element is just another way of testing the same thing- proper operation of the circuit, though I really don't think that's the problem.
 
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So far.. and I've only driven the 15 minutes it takes to get to work, I can definitely note a major improvement. It by no means idles as smooth as silk, but it is also not idling down really low and shaking the whole jeep. I also need to smell the exhaust see if it still smell funky. But so far it's looking good.
 
stephenspann27 said:
One more thing.. IAC is of course suspect in this situation, I've tried a J-yard one, and I now have a new one installed. When I was checking grounds, i tried to ohm out all of the contacts on the IAC plug (harness side) and all of the contacts read "open" shouldn't there be a ground among the contacts in the IAC plug?
Click to expand...
The IAC is a bipolar stepper motor driving a plunger. You won't get any continuity from any pins to ground, you will get continuity between two of the four pins, and between the other two of the four pins, and none between either set of two pins.

Sounds like you've mostly got this nailed, but to clean up the remaining roughness in your idle, have you tried cleaning the throttle body (and the IAC valve seat)? Between that and replacing my distributor cap/rotor, wires, and plugs I nearly completely solved my extremely rough idle problem.
 
kastein said:
The IAC is a bipolar stepper motor driving a plunger. You won't get any continuity from any pins to ground, you will get continuity between two of the four pins, and between the other two of the four pins, and none between either set of two pins.

Sounds like you've mostly got this nailed, but to clean up the remaining roughness in your idle, have you tried cleaning the throttle body (and the IAC valve seat)? Between that and replacing my distributor cap/rotor, wires, and plugs I nearly completely solved my extremely rough idle problem.
Click to expand...

Yes I've even swapped throttle bodies.. I had another "car guy" look at it today who has been around some 4.0's and he said it does idle "perfect" I'm just being too anal. And.. that I don't have piston slap.. that's just how a 4.0 sounds.. which confirms my suspicion. I listened to a friends '01 4.0 idle and it sounds identical to mine.

So I need to quite messing with it and be happy.
 
So you have confirmed that a bad heater in the O2 sensor can cause a bad idle. You are here by awarded one Attaboy! LOL. Congrates! let us know how the mileage does.
 
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