Codak

1999 sport 4.0L, AW4, 192,500 miles.

Ever since i bought my jeep it's been running great. But i have an intermediate rough idle problem. Only happens when engine is hot.
What happens is after startup i will be driving and the rpms will drop from a steady 800 rpms, down to about 500 rpms and jump around. This lasts about 10-15 seconds, then like nothing ever happened goes right back to 800 rpms and stays there. Will not happen again while i am driving.

I've read up on the forum seeing that it could be throttle body related so i
1) Took TB off and cleaned it well with TB cleaner.
2) Thought maybe it was heat soak so i bought the recall heat shield part from Mopar and installed it along with wrapping the fuel rail and injectors with heat insulation.
3) Replaced both TPS AND IAC then rest the PCM.

Did all this and the problem still remains, what else could fix my problem?

XJRed96

sounds like it could be an oxygen sensor. the problem would only be obvious when the computer is in closed loop after it warms up. any access to a scanner? any faults pending?These vehicles do have a tendency to have failing o2s. it's generally the front oxygen sensor that offers the most control over the fuel mixture so i would start there. The rear oxygen sensor is generally only used for fine tuning and Catalyst monitoring.

Codak

The whole time this problem has been occurring i have never had the check engine light come on until about 3 days ago. I took it to autozone and got it scanned

Code: P0135 O2 (B1 S1) Heater Circuit

I checked on the forum and some people said to replace the 15 AMP fuse in the engine bay, so i did because it was easy and reset the PCM. Light still has not come back on yet.

XJRed96

was the fuse actually bad?

if not then that could very well be your problem.

Codak

It was not blown, but i did look like it was half way falling out of the fuse slot. It was not securely in there so maybe i got the code because it was loose?

Also would cap,rotor and wires pertain to my problem? They look to be maybe original factory Mopar wires. Lol

XJRed96

If they do look original it would not hurt to replace them in the name of good maintenance, but I do not suspect that they will be your problem.

You can try unplugging the upstream oxygen sensor and see if the problem changes. but this will cause the check engine light to illuminate. The PCM will default to a "safe setting" so you might notice an overall drop in performance but if the oxygen sensor is in fact the problem of the surging then you should not notice it any longer.