Hi..I bought a 2004 bmw 330xi AWD in May of this year. Despite the O2 sensors Bank 1 & 2 too lean code that it produced when I first bought it, the car drove great for a couple months. But then, I gradually noticed my fuel efficiency, acceleration, and idling pattern reduce substantially. Then about a month ago, I noticed that my engine was getting very hot after only driving it for a short distance. The thermostat however never rose above the middle of the guage. Over the past few weeks, my coolant light started coming on every 3-4 days and I began having to add more coolant. There was no sign of any kind of leak from under the car. Then, about 2 weeks ago, after my car's engine would heat up, the EML/traction control/ABS/SES lights would come on and my car started stalling out whenever I put it in drive and gave it gas. It cranked fine but would stall in automatic mode and after heating up. However, It would not stall in manual mode or after a cold start. I checked under the hood and discovered a tear in the lower intake boot, which I replaced immediately. I hoped that had solved the problem. But for 2 weeks now, the car is still doing the same thing. I put it back on a scanner a few days ago and it said manufacturer control and camshaft position sensor bank 1 circuit malfunction. So last night I put in a brand new CPS...checked the codes...and no codes were found. Excitingly, I got in my car today thinking my problems were over...but alas, after I drove just a couple miles to the store..the warning lights came back on the dash. So I shifted to manual and made it home without the engine stalling. I checked the codes again and now it's saying manufacturer control 1500...which I read is that the IAC is stuck open. I removed the IAC a few nights ago...cleaned it..and put it back on my car. My question is this...could a failed IAC be what's been causing my engine to overheat and stall, or could it be something else? This car is not the cheapest when it comes to repairs and I do not have the $ to keep replacing every single part until I find the cause of the problem. If you could point me in the right direction or give me any advice on what to do or check, I would greatly appreciate it! Thank you!!! Sincerely, Katie G. 

Hi Katie

I think you have been treating symptoms not the problem. Did you cure the lean running? if not a lean burning engine will run hot which could cause valve damage and/or cylinder head issues. Which may explain the loss of coolant with out an apparent leak was this fixed? 

First I would get a BMW specific diagnostic tool  there are several available INSTA/INPA BMW 1.4.0  Carly for BMW (I use BMW 1.4.0) 

From your initial description I would have checked the Thermostats (x2) and checked the inlet for leaks (to much air entering after the Airflow meter will give a lean burn.

A BMW Diagnostic session is the answer to save your wallet more pain.

To help here are a couple of sites that may help (1) www.realoem.com This is a BMW Online Parts list to ensure if you are buying parts Used or New they are right for your car. Put the last 7 digits of your Vin into the Search box it will bring up your model. (2) www.newtis.info This one is a BMW Technical Information site Dealers use this site for "How To" Information. (3) www.pelicanparts.com A USA site with great "Hoe To" information with pictures.

Good Luck

Dave