I have been dealing with a rough idle and hesitation for about a year. My symptoms have progressed from minor to really bad currently.
In a nut shell here's what I'm experiencing:
• Really bad hesitation (like a shudder) for a few seconds only when applying light gas (maybe around 2,500 rpm and usually under load). Most of the time it is ok if you drive super slow with feather light acceleration and ok if driving it hard at WOT.
• This comes also with a very round idle. Minor sometimes...VERY bad at times - everything shakes and rattles. Sounds like it is going to stall out.
• Additionally, CEL lights with many codes. "Multiple misfires" (all cylinders), and "VANOS" codes. Clear codes and CEL stays off a few miles and then at one random time you give it gas and it hesitates they will all come back - in random order each time.
• Occasionally on cold mornings it will hardly accelerate at all. It just sputters and is barely drivable (is that limp mode?). I have to let it warm up, pull over and clear the codes and then it will run as described above - a hesitation only at specific times. I've learned to drive "around" it, so to speak.
Ok, now here's where it gets interesting! I've tried several things over the last 6 months to troubleshoot and finally gave up and took it to my BMW tech. One of the first things he tried was unplugging the mass air flow sensor. It was replaced last year, so I never even thought to look at it.
Magically, it runs near perfect with the MAF unplugged. I have since learned that it defaults to stored parameters if unplugged (it stumbles for a few seconds and then purrs like a kitten).
Great = needs a new MAF, right? Wrong!! I've now bought and installed 3 new MAFs and as soon as you plug one in = back to rough idle/hesitation/misfire codes. Unplug them = runs near perfect.
Ok, so wth is wrong when it does this when ANY mass air flow sensor is connected but runs fine without one???
FYI, I have done the following:
• Cleared codes.
• Smoke test = no air leaks.
• Die test = no oil leaks.
• Removed my Dinan stage 1 tune and restored stock.
• Removed foam air filter and replaced with stock paper filter.
• My mechanic reprogrammed it with a fresh copy from his INPA.
• Checked plugs and coilpacks (both new last year). VANOS solenoids new last year as well. MAF new last year.
• Cleaned fuel injectors (direct through the rail with cleaner).
• Replaced MAF (with 3 different new ones).
• Replaced integrated supply module (IVM).
FINALLY SOLVED!!! UPDATE INFO HERE:
https://xoutpost.com/1236219-post18.html