I was kinda putting my foot into my '93 535im yesterday passing 5k in 2nd gear when the acceleration went from strong and smooth to hesitating and not smooth. I backed off and the motor dropped to idle normally, but revving of the motor without load still produced vibration and stuttering.

It didn't feel healthy so I pulled off, opened the hood and listened to it idle. It seemed that there was some undesirable mechanical noise from the middle cylinders. A straight-6 running on 5 cylinders could feel like my ailing car does now.

Vital stats; 1993 535im, M30 engine, 162k miles. Stock except for a (great!) De Sylva chip. Oil changed regularly. Was half-way through a 25-mile trip; car was nice and warm. The oil light never came on, the temp gauge never moved, no cockpit indications that anything was wrong. Oil level was right in the middle of the range.

Possibly important; it blew it's head gasket about 2 years ago and I replaced it myself. I drained 11 quarts of coffee-colored oil/coolant mix from the motor before fixing it. I had the head machined flat and was pretty thorough putting it back together - after 2 years of problem-free running I thought I got it right, but I have heard that coolant in the oil can cause accelerated wear in crank bearings. The pistons and valvetrain looked to be in very good shape.

I accelerate in the car like this in 2nd all the time (I don't do it in 3rd anymore since that 67-in-a-40 ticket) ; it was not an unusual experience for the car.

I'm pulling the valve cover this weekend to take a look. Any ideas of what to look for and how? My best guess is that a valve spring broke. I'll check compression as well, then maybe pull plug wires individually to see if a cylinder is indeed dead, and which one.

TIA

Dave