rough idle and exhaust rattle

[jaimeson]

I have a 1991 318is e30 (135K), the car has recently been idling rough, there isn't a noticible difference on the tach but you can hear the engine pulsing and there seems to be morer vibration. Also my exhuast makes a metalic rattel sound when going from standstill idle for about 200 rpm and then the sound goes away. Any idea and what I should get done to it, i replaced the spark plug about 3000 miles ago and also replaced the coolant hoses. I am thinking the problem could be dirty fuel injectors for the idle and a loose exhaust bracket in the back. However the vibration and rattle problems go away once the car is over 1200 rpm's. You sugjestions are welcome, and i really don't care to take my car to the crappy bmw dealer in town.

[twinpop171]

The first thing that I'd do is check for vacuum leaks. Check the intake bellows for cracks, follow the vac. line off of the bellows towards the engine and you see where it connects into more lines. You can inspect these better by removing the bellows. there is 5-6 lines that are connected that will dry out and crack. Also follow the breather line off of the front of the valve cover and this will also connect to the lines too. Seeing the miles on your car they are probably bad. I've got 130k and just did mine, I know. Go to www.realoem.com and enter your cars info and look under intake for some diagrams and also under the water hoses. Two of these vac lines have a coolant pipe running through them. The cost of the lines is about $70 from the stealership but well worth it.

Also check into cleaning the Idle Control Valve (ICV). Do a search here on how to do it. Real easy, it is connected into the vac. lines.

Good luck, Dan.

[rxm6]

check motor mounts. i have the exact same problems and the rough idle wibration seems to be coming from a cracked mount, it may not be all of the porblem but it is some of it. for the rattle, has your exhaust gotten louder? i looked under the car one day and found that the bracket halfway between the cat and the muffle had broken off, I also found a 2 inch wide hold in my muffler. sounds great...smells horrible. ok...i'm being sarcastic about sounding great, i hate sounding like a coffee can civic.

[jaimeson]

Thanks for the advise, i will look into a vaccum leak, the reason why i don't think it is a cracked motor mount is that when the engine accelerates there isn't any vibration....

[manofsteele]

i can almost guarantee that the exhaust rattle you described is a loose/damaged heat shield for the catalytic converters. My car had exactly the same "rattle" problem. Solution-bang like hell on the heat shield to keep it from moving, OR (better solution) simply spot-weld the shield to the exhaust pipe-good luck