LUMPY acceleration and irratic throttle response... could it be my MAFs? - The Unofficial BMW M5 Messageboard (m5board.com)

LeatherMan · 20th August 2005, 09:16

As many of you know I recently replaced my clutch with the Spec Stage III setup including the aluminum flywheel. The car seems to run ok other than the horrific gear lashing sounds at idle. I still plan on updating my post /review of this modification, but I have run into a different albeit just as annoying issue with the beast. As some of you have experienced I recently noticed that in the mornings, or anytime the car is started after cooling down completely, the throttle response is slightly irradic and the acceleration is very lumpy feeling. I read that it could be my MAFs and so I followed the instructions on the board for cleaning them. It seemed to fix the problem for a couple of days, but now the irradic throttle response is worse and sometimes happens even when the car is fully warmed up. Also, the acceleration is incredibly lumpy when the car is warming up... definately worse than it was before. The final nail in the coffin was when I noticed that the beast would not rev out to redline in 1st gear as of tonight. It pulls hard up to about 6250 or so and then starts to cut out... it feels similar to the fuel shut off mechanism feels at redline. Does anybody have any thoughts or recommendations for me on this issue? Might I have inadvertantly ruined my MAFs by cleaning them as described on this forum? I have the Peake tool and it is not throwing any codes other than "Secondary Air System flow too low" which it seems to always throw no matter what.

Thanks,
Eric

standard · 18th August 2006, 19:21

Hi I have the same problem with my beast, I had the MAF's replaced under warranty but still no effect.The service guys cant find any fault codes or anything obviously wrong with it. The problems not so bad when the cars warmed up but very jumpy on cold. I think I will have to take it back again and suggest CPS.Will let you know how it goes.

ard · 18th August 2006, 19:30

Hey Eric-

I assume you have been following the work on the carbon block issue in the sticky... some interesting work arounds.

There seems to be a troika of 'driveability actors' on this motor:

MAFs to measure air flow and drive fuel, primary O2 sensors to adjust air/fuel, and CPS to adjust timing and make use of the fuel. (VANOS acutators come into play but not nearly as often.)

If you look back on hundreds of these posts, one of these items is often the problem.

In my book, MAFs and O2 sensors are disposables. You WILL need these one day or the other. I had zero codes, changed my O2 sensors at 50k and had a better running engine, so go figure...

Have you done fuel flow tests? (OBD unlock, read consumption as L/Hr up to redline in 3rd gear (watch the road too!))

A