I own a 1997 bmw m3 with automatic trans. The car runs great for the most part but when I start it up after a night of sitting it idles ruff for a few minutes then it's fine after that. the car does not really idle ruff if i start it a couple hours later either. So what do you think is the cause for ruff idle ?

My guess is the electronic coolant temp sensor...

it does have a message to check coolant level but it's full, I never would have thought it was a coolant sensor causing the ruff idle. Can you tell me why the coolant sensor is the cause?

On today's cars it acts much like the old choke on caburators! This is not the level sensor on the recovery bottle, it's usually on the block or head...

Also, try loooking at the air intake boot, and check for vacuum leaks. Please let us know, thanks for visiting 2carpros.com