Rough Idle

[Incantation]

Hey guys,

I have an m30 engine in my 1990 535i.. while having lent the car to my mother, the car developed a coolant leak and her not knowing anything about cars.. the car overheated and the head gasket went. Having a good friend who can source out bmw parts for cheap, i had all the gaskets changed, new bolts, new everything.. was about 1,200 in replacement parts alone.

Since my mechanics did the work.. the car does not idle smoothly.. to the point where I can feel subtle bumps here and there, even when the engine has been running for over an hour. The mechanic said something to the effect of that since the interior pressure of the engine had changed, it would take time for the electronic timing (or something) to compensate and that it would run smoothly after i had driven a while.. and it's been over 5000 miles and it's still bumpy.

Ideas? (other than getting a new mechanic)
Thanks for all your help, I really appreciate it.

[Martin in Bellevue]

I'd pull the valve cover for a look see & to check the valves. Also, pull the plugs & check them. Maybe the gaps are off, or one cylinder isn't firing its fuel injector. With the valve cover off, get the crank to top dead center & check that the cam timing is correct. Visually, there is a plane near cylinder #1 on the cam, that will want to be in plane with the tilt of the motor, ie, parallel to the side of the head.

Maybe find a reputable independent shop & have this stuff checked?

There seems to be alot of head gasket talk lately on the m30's.