I noticed a couple of days ago my 1997 740il seemed as if the timing was off every now and then, didn't think much of it. Now it runs rough and the check engine soon light is on and blinks. The only thing that I can say that I have done differently is change from 91 Octane to 89, I am not sure if that has anything to do with it. Before I cart it off to a mechanic and have to sell one of my lungs to get it fixed I thought I would pose the question to the group.

I noticed a couple of days ago my 1997 740il seemed as if the timing was off every now and then, didn't think much of it. Now it runs rough and the check engine soon light is on and blinks. The only thing that I can say that I have done differently is change from 91 Octane to 89, I am not sure if that has anything to do with it. Before I cart it off to a mechanic and have to sell one of my lungs to get it fixed I thought I would pose the question to the group.

Hopefully, it is just bad gas or water in the gas. I would get the codes read first and then go from there. Good luck.

Get the codes read. The CEL is always emissions related, and can point to: Cam position sensor, MAF, crankshaft position sensor, air leak(s), O2 sensors, and even a gas cap which has not been closed correctly.

First check the gas cap. It takes a few cycles to make it go away.

Then, check for air leaks on the intake manifold....starting in front of the MAF and working back. Some use carb cleaner to find the leaks. Do the research on www.e38.org

It is doubtful that the cam position or crankshaft position sensor is the culprit. Probably not the crankshaft posn sensor since the car starts. The cam position sensor could be the culprit if it has deteriorated sufficiently. These are easy to replace if you have two of them. Lastly, the MAF...most probably if the engine seems to be stumbling or hard to start. Usually gets better as the engine warms up, but not always.

Good luck.

jake