mtnboydl

All-
4.2L, 2012. When I first get in the car I've had some times where there's a rough start and rough idle for maybe 10 seconds and then it smooths out. No other engine problems. If I go into gear without waiting on it to smooth out it gets really jerky like a misfire.

I ran OBDeleven and can include the engine codes if you think they'd help, but they are all O2 sensor codes. There was a misfire code on a couple of cylinders a few months ago 1, 2, and 4. But those haven't returned.

Any advice?

MP4.2+6.0

First guess: High pressure fuel pump (HPFP), maybe on the same motor side as all the misfire codes. O2 codes for "Bank 1" would be tending to confirm the same--likely a lean mixture reading. USA passenger side for cylinders 1-4 on V8. You could search old posts for similar symptoms--any 4.2 FSI, whether D3, D4, old Q7 4.2, C6 A6 4.2, old S4 and S5 V8's, etc. From other posts and where they are (in plain sight) on y 4.0T, work seems straight forward. I have done it on a Golf R 2.0T but not the 4.2 or 4.0T FSI.

mtnboydl

Here are the codes. Looks like a little of both
edited for clarity

P017500 - Fuel Trim,Bank2 System too Rich
P017200 - Fuel Trim,Bank1 System too Rich
P209800 - Post Catalyst Fuel Trim System Bank 2 Too Lean
P227200 - O2 Sensor Signal Stuck Lean; Bank 2 Sensor 2
P017500 - Fuel Trim,Bank2 System too Rich
P017200 - Fuel Trim,Bank1 System too Rich
P219800 - O2 Sensor Signal Stuck Rich Bank 2 Sensor 1

KnappAttack

It sounds like what I had going on from about 50,000-100,000 miles. Rough idle that finally got cured with an intake port cleaning and walnut blast. I tried changing plugs, sea-foam in the gas, (yes I know it does nothing to clean the intake, it was more to clean the injectors and fuel system). After the intake port cleaning it finally cleared up and idled like a 8 cylinder. Now I'm sitting at just over 190,000 miles and the rough idle has not come back so go figure. I'm still planning to clean mine again when I get time this winter, as a have the oil filter housing needing o-rings and leaking oil too, so the intake has to come off for that anyway. This time I'll do it myself manually with no walnut blasting, just the good liquid carbon intake cleaner and manual wire brushing.

Also, don't "take off" prior to warming up and idling down coming off the rich mode. Like you found out when taking off prior to idling down it will run like crap. It's better once off rich mode, so let them idle down before putting it in gear.

How many miles do you have? My guess is it needs a good intake port cleaning. I'm not sure why they act this way with the intake carboned up like that, but they do. They seem to run fine once they come off the rich cold mode still.

MP4.2+6.0

If you want to try cleaning intake to see if that helps, try spray Seafoam in the intake. Then you reach the intake valves. I did the procedure on my 2010 Mini S FSI motor by introducing it with the provided spray tube clamped into an intake hose past any sensors. Assistant ran motor and kept it running while I gradually emptied whole can into it. Once I figured out where to introduce it, it was easy. Expect a rough idle while doing it and post can emptying until you rev it up some and clear out puddled spray in a big exhaust cloud. Expect a CEL/codes you then just clear. There are probably at least generic YouTube videos on it. In that case I was going after cold idle valve noise, which it fully solved.

mtnboydl

Sorry for my delay in responding!

So what I'm understanding from you two is that I need to spray seafoam into the intake slowly while maintaining a reasonable RPM? Where did you spray specifically? Right as the airbox plugs into the manifold?

MP4.2+6.0

Again, I did it on a Mini S, not a 4.2 or 4.0T. The basic technique is to find a place to introduce it that is past any sensors, especially MAF's or similar ones. For any V8 it would be before the intake has already branched to individual cylinders. A common one is you take the tube provided and clamp it into a hose connection like a big air tube, perhaps right at throttle body if it is post any sensors. Belt and suspenders is some duct tape over the tube area temporarily to seal off from a small vacuum leak around the tube under the clamp. Then two people, one to spray while the other is ready to work throttle/gas pedal to hold a fast idle--maybe 1500 rpm. It hesitates as you spray it in; sprayer can back off if it gets to where engine seems about to die. Shout commands back and forth over engine noise. After it eats the whole can, rev up with some throttle jabs to try to blow it through motor. It will be puddled in intake in some places. Then do a safe test drive where you expect it may run a little rough or hesitate at it works through. It should end up smooth. Clear any codes if it triggers a CEL; to be expected if engine is struggling some as it get pumped in.