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I had the same issues. I have done the following:
Replaced spark plugs.
Replaced two coil packs on bank 1.
Replaced ignition harness.
Dealer replaced my bank 1 HPFP.
Cleaned both MAFs and both TMAP sensors.
The cause for me was the passenger side high pressure fuel pump. Dealer replaced it.
I run stage 2 aggressive at 3.5 on 93. I've still experienced stumbles at idle, and I dyno'd well below stage 2 numbers the day before yesterday. It was 446whp/486wtrq, STD on a DynoJet just like Burger, so the numbers stunk.
I replaced the driver's side HPFP an hour ago. Easy swap out, and I negotiated BMW parts guy down to $160. One thing to note, I think you need to disconnect the battery because the LPFP periodically primes the line, so gas sprayed out every so often even though the lines were disconnected and depressurized.
Anyone with basic hand tools can do it. So if one of your HPFPs broke, you can replace it in under an hour. I'll bet you lunch your issues are NOT related to carbon buildup. They're trying to nickel and dime you to death. If you need any help let me know.
Grant
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