Chasing down a slight misfire on a 2000 540i

[Dan Wright]

So I've had this particular 540i for over a year, and throughout that year it's had a very consistent idle only misfire. The PO (a mechanic at a local shop) put a lot of time and $$$ into preventative maintenance, but claimed he could never figure out this specific misfire. The car feels excellent above idle, pulls hard, and drives as it should otherwise.

Things I know it's had in last ~3 years:
TC guides and tensioners
Valley Pan job
OEM Throttle body (brand new)
MAF
Plugs, boots, coils (I did plugs and boots myself again recently)
Injectors
Crank position sensors
Vanos solenoids
CCV
"All" vacuum and coolant hoses, brake booster pipe (this is a big claim I know)
Valve cover gaskets

Other items of note:
PO didn't specify if the Vanos seals were replaced, but the car has a rock steady idle and doesn't exhibit the other traditional vanos symptoms, best guess is yes.
The secondary air pump was "defeated" in some way physically, and then returned to it's intended setup in terms of vacuum lines by the shop I use. The car was throwing SAP codes (as you'll see in the pictures). I've since had the SAP and other emissions systems coded out by DUDMD.
The car has thrown a few misfire codes, specifically multiple cylinder misfire and individual cylinder misfire on cylinders 5,7, and 8. The issue definitely seems to be related to the driver bank.
Injection time is ~3.5ms in the pictures, but in the past I've seen it as high as 3.9ms.
Plug wells had very old dried up oil in them (pictures of the plugs included), but no fresh oil.
The increased idle speed is intentional and was done by Dima when I had the car tuned.

So I replaced the plugs and boots again myself recently, also swapped the coils side to side to see if the misfire would follow, didn't. I have access to a DIS/INPA GT1 setup, so I took pictures and a video to try and help diagnose the situation. Any input is appreciated.

[gmak]

The car has thrown a few misfire codes, specifically multiple cylinder misfire and individual cylinder misfire on cylinders 5,7, and 8. The issue definitely seems to be related to the passenger bank.

Aren't those cylinders on the LHS of the engine, or the "driver bank" in NorthAm? If you think that it is the passenger side, have you perhaps been changing coils on the wrong bank?

[Dan Wright]

Aren't those cylinders on the LHS of the engine, or the "driver bank" in NorthAm? If you think that it is the passenger side, have you perhaps been changing coils on the wrong bank?

Oh, you're right. I looked it up in the past but must have forgotten. I didn't replace the coils, I just swapped them side to side to see if the misfire/cylinder roughness would follow. Thanks for the correction.

[redd2k]

Did you ever find out what the issue was? Ive always had a miss as well but now its to the point where i really need to figure it out, same symptoms and on the drivers side

[whiteghost1]

Maybe primary O2 sensors?
Have you have them monitored while running to see if they are getting tired?

I too have a very slight intermittent misfire at idle only. Like you the car runs awesome otherwise, and I've done almost a mirror image maintenance wise. It's butter smooth when the engine is cold but starts to show the intermittent roughness when the engine starts to warm up and when hot.

Im guessing it could be my primary O2's but it's a guess, and I'm too lazy to check as it hasn't bothered me enough to troubleshoot.

[Dan Wright]

I took the car to my preferred shop to have a smoke test done to check for vacuum leaks. They found one between the throttle body adapter plate and the manifold, specifically the gasket between the two.

I'll be replacing the part in a few days and will report back on whether it solves my misfire.