2006 530xi, 180k miles, new fuel pump and fuel filter last year. Car was running fine till a few weeks ago it started running rough (seems like a misfire) intermittently after I filled it up with gas. The Service Engine Soon light comes on and off. I have not pulled the codes yet. Seemed to be most noticeable when accelerating from a stop and while turning corners or going up hills.

I thought some water might have gotten in the gas somehow so I put a few cans of Heet in the tank. Repeated the same process for the next fill up and it continued to intermittently have issues but never stalled.

Today I thought I would be smart and let it the gas run almost out. I drove it till fuel reserve showed "----" and then I added a couple cans of Heet and then I drove it for another 10 miles hoping to burn up all the water in the tank. During these 10 miles it ran rough the whole time. I then filled it up with 91 octane nonoxygenated gas and added another can of Heet. It ran good for a few miles but then started running rough again. I thought there might be a little water left in the tank so I drove it around for 30 miles hoping to work out the water but it ran rough the whole time and continues to run rough.

Engine idle:

Engine rev:

 

Code was cylinder #2 misfire. I swapped the ignition coils between #2 and #3 and swapped spark plugs with #1 and #2 and then drove around for awhile until the problem came back. The new code was #3 misfire so hopefully its a bad coil. I ordered new plugs and coils. I also added a couple bottles of Tekron fuel system cleaner to the gas tank.