My '90 E30 with the six cylinder M20 engine idles unevenly, especially when the engine is cold. A local mechanic said the mixture seems to be too fat but had no concrete solution saying I have to live with it.
But I think a too fat mixture kills the catalytic converter over time.
Is the mixture being fat the only reason for an uneven idle? Couldn't it be a leak on the intake?
How would you diagnose such a problem?