BMW Repair: 1999 BMW 318ti starting problem, coolant temperature sensor, fuel pressure regulator

Question

bmw 318ti Okay here it goes. I have a 1999 BMW 318ti that I purchased two and a half years ago in June. It had about 95k on it when I bought it and currently has 115k. It has been having an issue of turning over for awhile and then eventually starting, but extremely rough. Sometimes it shuts back off unless I hit the gas to get it to even out. The first winter it only gave me a problem starting every now and then. Last year it gave me more of a problem, so it was at the dealer over christmas while I went on vacation. It started for them everytime, so they couldn't diagnose it. This year it has been in and out of the shop since November 3rd. On October 31, 2008, it had a rough time starting and then the check engine light came on. I called the dealer and they said I can run it unless it starts running rough during driving. So, the following Monday I went to start it and it wouldn't start at all. It just turned over. I had to have it towed to the dealer and sure enough that Tuesday it started for them, but rough. Everytime I have had it to the dealer before this year, it never gave them a problem starting, so I would always bring it home and end up having the problem at home. I have had the run around with the dealer. Parts I have replaced: spark plugs, spark plug wires, fuel pressure regulator, air filter, fuel filter, coolant temperature sensor, valve cover gasket, serpentine belt and tensioner. The dealer checked the pressure of the cylinders while warm and all of them were within normal limits. So they went ahead and took the spark plugs out and let it sit overnight. The following morning they turned it over to see if they gasket was leaking through the holes. It didn't, so that was fine. They checked my injectors to see if they were leaking. They were all fine. They lastly checked the pressure of the cylinders while cold and there was no pressure in cylinder number 3. So they are telling me they piston rings are not sealing, but if that were the case, wouldn't the car have white smoke and have worse gas mileage and acceleration? I haven't had any of those problems, so I'm wondering if they are just saying that is what it is because they can't figure out anything else. I am so frusterated with it. I started it today...it started rough, but started and my check engine light came again. It was also sitting in the sun. I tried to start it at 9pm and it wouldn't start again. I just don't understand what is going on. I don't want to replace the engine if it isn't really the pistons. I love this car and don't really want to get rid of it, but I need something that is going to start every morning. I don't live in an extremely cold environment either...Pennsylvania. It always starts fine when it is warm. I would also like to add someone had rear ended me into another person on January of 2007. It cost about 7 grand to fix it. I don't think that really has anything to do with the problem now, but just to let you know.

Answer
Hello Heather sorry for not getting back to you your problem has given me lots to think about.I have had a 318i in my shop the past few days with your same kind of problem.There is slightly one difference and that is the car is here. The test I have done a compression test,fuel pressure test,all the basic adjustments ie.throttle plate,valve adjustment.
My problem seemed to be bad hoses(being wrong type and collapsing)although I think the throttle plate was at fault.You said they said a cylinder was 0,well that does present a problem.I don't think rings are at fault.A cylinder leak down test will tell you where the problem for sure is wether it is rings or valves.If it is valves which are at fault,this would be skipping badly.The thought of white smoke comes only if it is coolant related.The dealer(?) telling you its ok to drive with a check engine light on is NOT the place to go.They should know better.If the light comes on there is a problem and where you experience a problem they should have had you come in a diagnose the light coming on.This would tell you also if the engine needs replacement by determining why the light came on.
So my advice find a place that is more reputable and know something about BMW's