smoke/exhaust from exhaust pipe

99 XJ

I installed the APN exhaust header a while back. I have the 98 head, so I didn't have to file down header to make it fit. It slid right on and was very firm fitting.

I've been chasing rough idle and I am pretty sure it was an exhaust leak at the donut. I could tell it was kinda at an angle and the RHD side had a much alrger gap than LHD. So I double-checked all of the bolts on header, and then loosened my exhaust hanger and reseated the manifold to downpipe flange. It fits much better now and is very evenly and tightly pressed up against donut.

I started it up and it was smoking a lot from what seemed like below the flange.

There is lots of old oil and residue on the transmission pan(?) right where the exhaust pipe turns horizontal and goes from LF to RH side. This seemed to be the area where the smoke was coming from. And it was not fast moving, hard to see exhaust, it was like whisping white smoke.

Is it possible the exhaust gets hot enough right there to kind of vaporize the oil/gunk right up next to the exhaust pipe?

I really can't figure out this rough idle issue, and I no longer think it is due to an exhaust leak. Engine feels great sitting in P or N, but very rough in gear. No issues when driving. Thinking I am going to take it to a transmission shop next for an inspection

Exhaust gasses can range from several hundred degrees at idle to +800 degrees under heavy loads. Jeep 4.0L with oil leaks are very common.

Are all the tune-up parts fresh ? Have you used some fuel injector cleaner recently ? Have you tested the injectors ?

What are the RPM's when the idle is OK? What are the RPM's when you think the idle is rough ? Is it stalling ?

Tim_MN said:

Exhaust gasses can range from several hundred degrees at idle to +800 degrees under heavy loads. Jeep 4.0L with oil leaks are very common.

Are all the tune-up parts fresh ? Have you used some fuel injector cleaner recently ? Have you tested the injectors ?

In the past year I have put new spark plugs & coil, distributor w/ cap and cables, new fuel injectors (4-pintle upgrade bought from motorman on ebay - though they sat in the garage uncovered for 6 months recently so they could be dirty - would seamfoam through the tank take care of this?), new harmonic balancer, timing chain, motor and trans mounts, and a lot more. I also disassembled the intake and thoroughly clean it along with IAC and its port. I recently pulled each fuel injector in series and the idle got worse each time, so it seems they are working fine.

I ran seafoam through my gas tank not long ago. I'm thinking about doing the brake booster/intake cleaning method next. I'm sure its gummed up in the cylinders - especially after sitting 6 months.

What are the RPM's when the idle is OK? What are the RPM's when you think the idle is rough ? Is it stalling ?

The RPM is ~1000 on cold start and the cabin is very smooth. It slowly comes down to 700 and is stable there. Occasionally it shudders and the RPM needle will nudge and there is a loud surge of vibes/noise in the cab, but for the most part its dead-nuts at 700 whether its rough or not.

No stalling or loss of power. No issues at highway speeds or anything else. Just cabin shake when sitting in gear with my foot on the brake. If I'm in N or P, or even just rolling it is very smooth.

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It seems a bit better after redoing my manifold to downpipe, but still rougher than I would expect. I see lots of people with the rubber BD MM saying the vibes aren't much worse than OEM.

Getting frustrated, and think I'm gonna put a new IAC in. It's still stock with ~188k on it. Wouldn't hurt to just replace IMO.

EDIT: I will also say it was very smooth this morning when backing out of the driveway, then it seemed to get worse as the car warmed up. Not sure if that is indicative of vacuum leak or what

A new genuine Jeep IAC may help. The Jeep 4.0L isn't really known for a smooth idle, especially with higher miles. If it doesn't stall, or the idle does not fluctuate wildly, I would call it good enough.