Topic: rough idle and stalling issues Need some ideas

[stan98tj]

Jeep's been experiencing a rough idle for some time. Usually a quick tap to the gas pedal clears it up and she drives just fine. Recently however, shortly after starting from a cool or cold engine, the Jeep will begin to idle very rough while I begin to drive, then it will bog and basically stall out. While this happens there are a series of popping sounds from the exhaust. When it first would happen, I would be pushing down the gas to see if I could "power" out of it and it would finally catch and drive off. Now however, it requires me to stop, turn off the motor and start up again. It then drives fine. Basically as it happens, there is a severe drop in power no matter how much I push down on the gas, the exhaust pops over and over and the jeep basically feels like it's about to stall. No check engine light.

[sharpxmen]

a bad signal from O2 sensor could do that, but so is MAP or tps. Hard to tell without more info though (thinking about it a squirting injector can cause that too).

[stan98tj]

Would a bad O2 throw a code?
No codes for now, but cutting the engine and starting over seems to get it back in working order. The other day however, it kept rough idleing in "Park" but was fine in "Drive". No matter how many times I tapped the gas, it didn't help.

[sharpxmen]

i've heard that it can give bad info without a code, I think JF had this issue recently.

[stan98tj]

Had a lot of start ups these past 2 days, only bogged once and I was able to power out. It's just a bit annoying and concerning as I don't want this to happen if I am trying to merge in a hurry....

[Tr00b]

Try cleaning your intake air temp sensor.

[Bounty Hunter]

Bad gas maybe?

Have you tried giving the throttle body a good bench cleaning?

[jfrabat]

i've heard that it can give bad info without a code, I think JF had this issue recently.

Yup.  My O2 was bad, similar symptoms, and no code was thrown.  I have also had something similar happen once I left the TPS unplugged, so you may want to check that (I would start there, as it is easy, but my guess is the O2 sensor).  And the power bog will only get worse (and typically, at a REALLY bad time, like when you are accelerating to cross a road or something), so you may want to have it checked out sooner rather than later.

[sharpxmen]

fuel pressure is the other thing i would look into.

should at least pull the plugs and check them visually (are they wet or white) - might give you an indication if its running rich or lean when this happens or if it's one of them that is visibly different then you might know if its running in 3 cyl for example.

[neale_rs]

This reminds me of a Neon that was behaving similarly and it was the spark plug wires shorting to ground sometimes.  Look at the engine running in the dark, you might see some sparks.

[jfrabat]

I sure is sad, but I have had ALL these things happen to me!!!  Shorted spark (spark was going from Cyl 1 to the AC compressor), bad fuel pump, bad fuel filter, bad FPR (you may want to check your fuel pressure to start diagnosing; if you have the meter, it's free), bad TPS (well, it was a plug), bad O2 sensor, bad MAP sensor...  Oh, and NONE of these issues threw a code (well, the TPS did, but none of the others).

[stan98tj]

Guess I got a little work to do. I'll keep this updated.
Heres a question about this, do any of these possibilities get better as the motor warms up? Basically this happens at first start up or shortly after, shut it off, start again and once it warms up, it doesn't happen anymore.

[sharpxmen]

that could be related to temp sensor, but if it was that bad it should throw a code. the other thing is if you live in an area with high humidity and a lot of condensation in the morning it might be worse before it warms up if its spark related (if its some wire or cap/rotor issue)

[Tr00b]

I had this same issue. O2 sensor upstream of the cat with a new exhaust manifold and manifold gasket fixed it. However the intake air temp sensor is downstream of the pcv vent from the valvecover into the intake manifold. It gets wicked gunked up and causes issues and needs to be cleaned specifically. This is unique to the 4 cyl models only I think most of the 4.0 ones I've pulled were clean.

[stan98tj]

So should I start by replacing the O2 sensors right off the bat? What about a misfire? Would it be misfiring continuously or is it possible to have a misfire only initially upon start up and then have it clear up?