I have a 2004 jeep that I put a 1999 5.9L in. The motor is a reman. I've replaced the tps, iac, temp sensor, intake temp sensor. I've done the intake upgrade. If I let the vehicle idle it's fine at first then the iac opens up and it bogs down until it stalls out. Drives fine at hiway speeds but when I stop at a red light it wants to stall. I've read the forums and seen a lot of the same issue but have not found a helpful solution.

 

It's probably the oxygen sensor rather than the IAC. Let me guess: Starts up just fine when stone cold, but shortly afterward begins to stumble and make a lot of induction noise (sucking sound in the intake), right?

You could just replace the pre-cat oxygen sensor because it needs doing, but you can test it first if you'd like. Just unplug the thing and see that the symptoms stay away. But don't run like that for long once it's proven.

 

I'll give that a shot. The o2's were both replaced with the new exhaust about 1k miles ago but I know that means nothing.

You are correct about the sucking sound from the throttle body. Only does it when it starts to warm up.
I'll give that a shot though. Thanks.

 

I forgot to mention: Get only dealership, Denso, or NTK parts. The others don't agree with our trucks' constitutions.

 

Well I already replaced it. Bosch I believe. It was all they had.
It seems to be idling better but seems to have a hesitation at low rpm's now.
Is there a relearn period?

 

There is a bit of learning period there, but things might get worse because our trucks hate Bosch oxygen sensors.

They're fine parts, but their response time is much faster than our PCM's are designed to work with so we get lots of sampling errors that confound things. One of the symptoms just happens to be hesitation at low RPM, accompanied by erroneous random misfire codes and a greater tendency toward preignition.

 

Sounds good. So I need to take it take it back and get the right one. I'll update when I'm done. Might be a couple days since it's not real easy to get parts where I am. Thanks again for the help.

 

Update, picked up an ntk o2 sensor and installed. Seemed to be working better last night. Drove it today and it was doing the same thing again. Any other ideas?

 

Did you reset the PCM after replacing the sensor? (PCM needs to learn the NEW sensor, not figure out that things are different now.... that takes longer.)

How about the IAC? How old? Cleaned lately?

 

I did reset the pcm and the iac is new as of a couple weeks ago.