dawid_w

It is a very easy job.

See the post

https://5series.net/forums/topic/853...ssion-no-more/

pauliehcfr

The thermostat most likely cured the rough idle because the engine probably wasn't warming up to operating temperature. There is a coolant temperature sensor on the thermostat that sends the reading to the DME which in turn makes adjustments to engine operating parameters based on many things, one of them being coolant/engine temperature. If it continuously saw the coolant as being cold, it would most likely adjust the engine to run rich which would cause some rough idle issues, black smoke from exhaust, etc. Also, it may nit have been going into closed loop operation whereas the O2 sensors become active and the engine runs on inputs from various sensors as opposed to running on preset values. BMW had a problem with earlier thermostats also known as MAP cooling, in which they would fail, cause a check engine lamp an some driveability issues. The fix was to replace and recode the DME...

shorttough

HEY, i had the same problem, i know EXACTLY WHATS WRONG WITH YOUR CAR.

There is a crank case Valve and its made of rubber get those replaced, its causing the vacuum to be leaked, go to any indy & buy the part from bmw its a orange color valve. and it will fix your issue.

Duncan545i

I have a 2005 545i and just had new water pump, my mechanic, who is very good suggested a new thermostat at same time. This he did, I drove vehicle about 10 miles then got excess emissions and check engine light. Took car back to garage and explained, he hooked car up and said I needed new O2 sensors, I said it was a real coincidence, he cleared the lights, and ran the car for 2 minutes, the lights came on again and he said he would check again, this time a thermostat fault.....new stat again and this time lights are off and have been for 100 miles....I obviously got a dud stat, fortunately no O2 sensor needed. I assume that the dud stat somehow triggered the O2 sensors