Re: '94 740iL with new engine,idles rough (archive)

I spoke with a mechanic and he said that my "rear crank case plate" needs to be replaced to stop the rough idle that I am experiencing. I don't know what he is talking about. I have the new engine in it and I also replaced the O2 sensors because the check engine light came on and said that the O2 sensors were faulty. After I replaced them the problem continued and I had smoke coming out of the tail pipe. The mechanic said that it is fairly common problem. What I want to know is what should I replace to get it to work right. Any comments would be appreciated beforeI take in to that mechanic for a $400 repair he said it would cost me.

There's a PCV type diaphram on the backside of the intake manifold. It's a common problem for this to leak vacuum and cause rough idleing. Normally this is caught before you get to the engine replacement stage but you might want to check it first. You can carefully put your hand over the valve while the engine is idleing and tell if it's leaking or not.

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