Rough Idle-Help!!!

I have a 2003 325i BMW. Recently, it started to idle very roughly. When placing the care in reverse the engine idles up and down in short intervals. Sometimes, it even shuts off on me. This also happens sometimes while stopped in traffic. I have replaced the DISA, fuel filter, ignition coils and spark plugs and the problem remains. I took the vehicle to a secondary BMW shop for a diagnostic. The mechanic had a $10,000 diagnostic tool, but I wasn't too convinced that he knew how to use it. At first his computer read that I was misfiring on all cylinders. While running diagnostic on my car, all of a sudden the car started idling OK. I also noticed that the System Engine light had gone off. I ask the mechanic if he cleared the codes and he said that he had not, that maybe the machine fixed the problem while running diagnostics. Then the guys computer gave him some type of code that which he interpreted as a bad throttle foot pedal. Sounded strange to me...but that's what he said I needed. I gave the guy 20.00 and went on my way. The car ran fine all the way home. After I got home I shut off the engine and restarted the engine....and what do you know....the rough idling came back. At this point I am at the point of taking the car into the dealer......I am I so fearful that they are going to stick it to me. Do you think it would worth it to take it the dealer and pay them for running a diagnostic?

Maybe the scanner fixed the car? LOL. I sure wouldn't be taking it back there!! Sounds like a very common issue on which there are hundreds and hundreds of threads you can search and learn from. Vacuum leaks are extremely common and can often cause this exact issue, misfire codes, along with lean codes, idle hunting, etc.

Surging idle can, in fact, be due to a faulty throttle position sensor either in the pedal (must replace the whole assmebly but a very easy DIY), or in the throttle body itself on the intake manifold (more involved and an intermediate DIY). I'd say the code is probably right. Start with the pedal and search for a DIY I think it's a couple of screws, a plastic clip and unplug the assembly and remove. Install is reverse. that easy.

I was just about at the point of taking my car to the dealer to have them run diagnostics before I was referred to a mechanic with a MODIS diagnostic computer. To make a long story short, the mechanic ran the diagnostic and got a P0171 and P0172 code I believe. He then connected his smoke machine to my engine to check for vaccuum leaks. It took him about 45 minutes to pinpoint the exact location of the vaccuum leak. I would have never seen it. I happened to be a hole in my pcv hose. The PVC hose was located beneath the DISA on the other side of what looked like a water hose. BMW wanted to charge me $104.00 for a PVC hose. The mechanic was able to remove the pvc fitting and put it on a new hose. After replacing hose and resetting codes......wha-laa.....no rough idle. They only charged me $85.00. Thanks for your responses.

Thanks for coming here and updating your thread. Most of the time when new members find the fix, they fall of the face of the Earth; you wold never hear from them till the next time they have an issue.
Good job on following up with us.
If you wouldn't mind, could you be more specific as to which CVV (PCV or oil separator) hose was leaking?

You might want to check this...

http://www.jaghelp.com/2013/01/that-...ough-idle.html

I am an experienced mechanic, and you always try the cheapest ways first. In other words, there may be a number of things wrong with your car, but first you try the cheapest. In this article there is a list of cheap things you can try yourself. Best of luck!!!

This works well also ...
- How to diagnose a BMW engine misfire (1) & a cold-engine intermittent misfire (1)

Well, he already fixed his problem...