Rough idle trouble shoot thread

[Nickfpharmd]

Hey all. I know this has been discussed before, but am looking for some help with next steps.

2000 TJ
4.0L
5 speed manual.
93k mi
Bought a few month's ago

Was previously having the rich gas situation (black soot from exhaust, check engine light, RPMs dropping very low at traffic light once warmed up, terrible gas mileage, poor acceleration).

So far here’s what I’ve done:
Gumout fuel system cleaner a few hundred miles ago
Gumout 6oz in oil a few hundred miles ago
02 (B1S1) sensor replaced with NTK23122.
New plugs (APP985)
Took off and cleaned TB
New Mopar TPS (4874371AC)
New Standard Motor Products IAC (AC176)

Acceleration seems better. No bucking or jerking felt after a test drive at some higher RPMs. However, idle still seems a little rough. RPMs at start up are around 750 and bounce around a bit between 500 and 750 when idling.

The MAP looked original. The lines all look in good shape, but haven’t tested for leaks. Was told the fuel pump was recently replaced by previous owner.

Would love to hear what the group thinks. Is replacing the MAP worth a shot? Thanks team!

 

[macleanflood]

Plugged cat?

Does it run better without the O2 sensors? (Basically creating an exhaust leak around the cats...granted it will throw O2 codes.)

-Mac

 

[Jerry Bransford]

Does the engine run smoother when it's cold and then starts running rougher as it warms up? If so you have a bad Upstream O2 sensor. If you decide to replace your Upstream O2 sensors go strictly with NTK, NGK, or Mopar. Avoid Bosch and store-brand O2 sensors.

 

[Nickfpharmd]

Plugged cat?

Does it run better without the O2 sensors? (Basically creating an exhaust leak around the cats...granted it will throw O2 codes.)

-Mac

Haven’t tried this, but will try it soon. Have you ever tried testing the temp differential between the pipe pre-cat and pipe post-cat? I read that if the post cat temp is significantly cooler than pre-cat, it points to a potential blockage. Any thoughts on this?

 

[Nickfpharmd]

Does the engine run smoother when it's cold and then starts running rougher as it warms up? If so you have a bad Upstream O2 sensor. If you decide to replace your Upstream O2 sensors go strictly with NTK, NGK, or Mopar. Avoid Bosch and store-brand O2 sensors.

Thanks Jerry, but already replaced the upstream O2 with a NTK.

 

[macleanflood]

Haven’t tried this, but will try it soon. Have you ever tried testing the temp differential between the pipe pre-cat and pipe post-cat? I read that if the post cat temp is significantly cooler than pre-cat, it points to a potential blockage. Any thoughts on this?

Absolutely...got a IR laser temp gun? I'd get engine side of cat, cat, and tailpipe. If I recall correctly the cat is supposed to be 30 degrees warmer. Don't quote me on that.

-Mac