Junior Member, warming up (<31 posts)
Join Date: May 2011
Location: Istanbul Turkey
Thanked 6 Times in 6 Posts
I have a similar story.
Does your car increase idle frequently at normal operating temp., like it does at cold start to heat the cats? Up to 900-1000rpm and change exhaust sound. Mine m6 had this problem when I bought, also check engine light was on. I have checked the error codes, and found that thermostat and water temp sensor were faulty. I replaced them along with the vanos solenoids (The test result was 0.45-0-50). Now no error codes and CEL does not illuminate. But the idle problem is still existing. It looks like the car is trying to heat up the cats. Two options wrong signal from the sensors or inefficient cats like 1hotm5 says. I was trying to figure out if it is catalytic converters that cause this problem, I found your thread.
If you have idle problems like me it seems like you have faulty cats. I will check the O2 and temp sensors at the exhaust. If they are ok too, I would conclude my problem as cats, too...
If it is the cats, the reason shoud be found.
High oil consumption, (mine consume 1l/1000miles)
Faulty temp sensor (like mine)
any other suggestion will be appreciated, since I am also not 100% sure with my problem..
By the way this is my first post in this forum so hi to everyone who is reading.