RPMs erratic until warm up

[The shuggs]

I've been dealing with a reoccurring issue where on start up my RPMs are erratic. It started where it would idle fine, and stumble under accelertion until the engine warmed up. It was worse the colder the outside temperature was.

It progressed to where it would idle erratically until it warmed up. It also threw a p0121. I unplugged the TPS and it idled fine, so I replaced the TPS (with a Mopar one). It solved it for a while, but now the problem is back.

Is there a possible concurrent problem? I'm out of town for work, but want to get ideas to check before I get back. I'll definitely check the new TPS.

Could a vacuum leak or bad ground be the culprit? It was warmer outside when I put the new sensor in, so it could have been fine when I was replacing the sensor.

 

[Jerry Bransford]

My bet is you have a faulty intake air temperature (IAT) sensor always telling the PCM the engine/air is warm even when it's still cold. When the PCM incorrectly thinks the air is warm (less dense) than it really is (like if it was actually cold/denser) it would set the air-fuel mixture incorrectly.

 

[The shuggs]

Thanks for replying. That makes sense, I'll look into that. Is there a possible code that it might give. My odb scanner has some live data, so I might be able to check it.

Also I think my tps should be fine. It sucks to have spent money without fixing the problem, but hopefully I can use it as a spare. Especially since Jeeps aren't the most reliable electrically.

 

[Jerry Bransford]

Like bad O2 sensors, the PCM can't always detect a bad IAT sensor.