Quote:
Originally Posted by fishhouse4
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).
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Long overdue update to this issue that I believe I have finally resolved.
My X5 was parked for the last 2+ years at a buddies house - I bought a new car so it was a spare at that point. He is a part time mechanic and was supposed to be looking into this problem for me.
He never gave it much attention, so I got it towed back to me last Fall to continue troubleshooting myself. Then a month or so ago with the help of a mobile mechanic = we finally figured it out!!!
Turns out that ALL of the issues traced back to electrical/wireing issues to the components in the dry box in the engine bay. Specifically:
• Water damage/corrosion inside the DME/ECU, VVT and IVM modules. All looked fine from the outside. But once opened up they each had major corrosion to the circuit boards inside. So at some point(s) water was able to get inside that storage box and drench them.
Solution was to replace IVM module (cheap...already had a spare from previous troubleshooting), replace the VVT (cheap...used one from ebay) and had the DME sent off to "The ECU Pro" to be tested and cloned to a new module (not cheap... ~ $800).
• Various broken/missing/damaged/loose pins and plugs on the wiring harnesses for those modules. For example, IVM had some pins that were pushed in, VVT had a bent pin, DME had some female ends of the plug that were too loose/stretched open. All of these lead to them not making proper contact once the harness was connected. Probably all my fault when I was plugging stuff back in at different times years ago.
Solution was to repair pins by straightening them out and/or pulling pushed in pins back out. I also replaced the plug ends of 1 of them with a donor engine wiring harness that I already had - since a full engine harness swap was the next step on my list to solve (fairly cheap, ~ $250 used from eBay). I cleaned all the female plug holes in all of the harness plugs as well to remove any potential corrosion.
After doing all of that she started up and ran like a dream!
4 years after first starting this battle = I have no codes!!! 
Several others had similar issues a few years ago when I first posted this, so I thought I would share my experience.