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2006 M5 Alpine White
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Three things come to mind to check before committing to pulling the valve cover. You mentioned it runs fine when warm and even at high RPM so I doubt it would be a valve spring or a VANOS solenoid (although I'd be willing to bet your solenoids fail the test)
1) Scope the cylinder like what @amesser325 said. Look down both the spark plug hole and throttle body.
2) Check the wiring for both the ignition coil and the fuel injector
3) Since it runs fine when warm it sounds very similar to symptoms I had a few months ago. I had misfires on cylinders 2, 3, 4, and 5, so all on bank 1. But on bank 2 I only had a misfire on cylinder 7. It had only been a year since I replaced all the plugs and coils so I was fairly confident it wasn't any of that. The key difference is that I had some catalyst codes and the misfires were pretty specific stating "DME: Misfire impairing exhaust emission, cyl. X" which was code 002B46 for cylinder 5. When you get a chance let us know the exact code you're getting.

If your misfire is the code in #3 then the remedy is to gut the cats and get a tune :cool:
 

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2006 M5 Alpine White
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120 Posts
You may have hit the nail on the head… I know my cats are bad. I smell them lol. No codes from them though for years. UNTIL a week ago. I got these ones. I cleared the codes and they haven’t came back.
P0430 and P0420 Could this be it!?

I also noticed earlier when I was driving in realpt Low rpm it gives a little sputter feel. But on wide open throttle… again car runs fine.




not familiar with the term SAP? Sorry. What do you mean? I will answer.
Hmmm. I never smelled gas but I did have error codes for "Catalytic Converter Conversion" on both banks. I would clear them, they would go away for a while then come back eventually. I got tired of this after a few months and decided to take the plunge into the cats.

Your error codes seem to be generic and not BMW specific. Do you have ISTA or INPA available to you? Here is a screenshot of my fault codes read in ISTA

Font Rectangle Screenshot Number Parallel


Could very well be the SAP too, but I'm pretty sure you would get a code for that.
 

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2006 M5 Alpine White
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120 Posts
Yes after the car is warmed up. I restart it and the issue goes away completely. And the check engine light goes off.
Interesting that you get a check engine light... Or maybe interesting that I did not. How long do your misfires last during a cold start? Mine were only ever less than 5 seconds as the RPMs would bounce quickly then smooth out around 1200. Then after another 5-10 seconds start steadily dropping to a normal idle.

Either way, when restarting the engine warm I had no issues either.
 

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You fixed yours correct? what was it?
Mine was fixed by gutting the primary cats and getting a tune, so I can only assume the misfires were due to clogged primaries.

It'll misfire and idle really rough until it's basically warm. So 8-10mins? restart car after that and all is good. Idles smooth, no more misfires, runs good
This is WAY longer than any of my symptoms persisted so I don't think we're comparing apples to apples anymore. @platii mentioned your compression seems low compared to spec.
What do your other cylinders measure?
Was that measurement taken cold?
Could you measure it warm and compare?
 

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2006 M5 Alpine White
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120 Posts
Correction:
The minimum compression is 6.5 bar= 94.28 psi.

The TIS doesn't mention to warm up the engine.
Generally performing cold compression test gives more accurate reading if you are in diagnosing mode. Activate the starter for 8 seconds to test for compression.
Agreed. However my thought process was that it appeared low when cold and ran rough cold but ran fine after warm. So comparing cold and warm could tell us something. It sounds like all the cylinders are testing similarly, however, so probably not the case.
 
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