2008 s6 nightmare engine twitching jerking
 

Hello, recently bought audi s6 after driving just 20KM got check engine when got home after 300KM obd scanner showed cylinder 8 and random cylinder misfires (current) and cylinder 6 misfire (pending) P0300 P0306 and P0308, cold engine started roughly and showed random cylinder misfire pending fault and cylinder 8 5 and 4 pending misfires. Got to service they changed coil pack for cylinder 8 and test drive car from 0-100KM/h all was good 5.4s no twitching all OK, before was twitching when go on full throttle. Next day started car again cold engine work roughly no check engine though. Next day started check engine got cylinder 8 misfire current. Again engine twitching on full throttle. In service told fuel pressure too low but they did not have instruments to measure actual fuel pressure for high-pressure pump. I will go to dealer after 2 days.

i was to diagnostic at other mechanic and computer showed pending P310B code something with low fuel pressure. they cleared error and then I went for test drive again car was running just fine with full throttle.

next I was at audi dealer and they said need to replace low fuel pressure sensor I replaced it and no changes at all after test drive again got error P310B Low Pressure Fuel regulation: Fuel Pressure Outside Specification.

annd now I'm furious as hell!!! Hope someone can give some good advice...
Dealer changed some other sensor at the bottom somewhere not sure what it called it cost me $650 labor was expensive $400!!!! And result seems is ZERO!!! Again twitching at 5000 RPM and up they now telling me that something wrong with gearbox I think it's Pure BS they just want again do some sh.t and charge again I have never heard for such automatic transmission problems that car jerking at 5000 RPM no any vibrations etc and that it could be automatic transmission problems what do you guys think???

The cold start rough idle is intentional for the 2008 5.2L V-10 to warm the cams, oil and other fluids. As long as you aren't having new codes I wouldn't worry.

Misfires can be caused by carbon deposits on the valves. The V10 was one of the first engines with direct injection. As a result there is no fuel washing over the intake valves and they develop carbon deposits. Carbon cleaning is needed to solve the problem of loss of power and misfires.

Had the same problems. Changed my hpfp's.