AUUUGGGHHH!! SES and rough engine. Not now!!
 

2003 X5 3.0i

Trying to get home to New England for the holidays. Drove all day from IL to Dubois, PA with no problems. Filled the tank from near empty (mistake, I know) mid-afternoon. Stopped for dinner around 7:15PM and came out about 45 minutes later, started the car to find a rough idle. Two seconds later the SES light comes on. Pitch dark here and I'm no mechanic anyway, but I don't see anything wrong. No fluids on the engine or the ground, belts are fine. Oil is full (checked it yesterday). I'm thinking water in the gas maybe. 45 minutes would be long enough for it to freeze in the lines at 20F ambient, right?

Any other initial guesses? I opened and closed the gas cap again, just for luck. Didn't matter. Talk about crap timing. The only good thing is we were right at a hotel, so at least we're not stranded beside the road. Nearest BMW dealer is in State College 50 miles away.

When it had the rough running start was the SES light flashing at any point?

I didn't notice the SES right away. After the initial rough idle I shut it down, then restarted. It wasn't until I'd turned it off and back on that I saw it. There was no SES before we stopped. In fact, in the nearly 100k miles I've put on it, this is the first time I've seen the SES light.

it seems you had a bad luck with the gas quality....

Try disconnecting the MAF sensor and see how it runs.

I'm ashamed to say this, but I wouldn't know the MAF sensor if you hit me over the head with it.

EDIT: Ok, I looked it up. I think I know where that is. I'll try that in the morning. What should I expect? Will it run worse or better if the problem is the MAF and I disconnect the sensor?

If it is a failed MAF it generally will run better. Might not idle correctly but certainly drivable. Easy to change as well. It could be anything, but I always check the easy things first if you don't have access to a code reader and someone to interpret it. MAF failure is pretty common and having experience in very cold climates, I know for sure many us BMW owners have that issue. Also check to make sure the airbox is tight and fitted properly.

Thanks. I'll check those things in the morning.

So here is (was) the problem.

According to the SM at the State College, PA dealer, this part had failed some time ago on my X5, but it didn't seem to affect the engine at all. Then the other night a valve in this piece actually broke off and caused a vacuum leak, which caused the engine to run too lean and misfire. They didn't have the part in stock and I couldn't wait another day, so they removed it completely and somehow bypassed it. I have an appt with my dealer shortly after we get back to have it fixed properly.

Engine runs fine now, though. Not sure what this part does if it runs fine without it.

Thanks to all who replied here. I appreciate the input. I was dreading some seriously bad news about this, but it turned out to cost me only some time and less than $200.

http://www.bimmermail.com/part.jpg

I read about a free repair for this item on E46 Fanatics: 3-Series, BMW Forums, BMW Modifications, E46 BMW.