I have done just about everything I can think of to get my idle on my '91 745 Turbo up to where it is supposed to be, but it remains at600 or 650 (700at the very highest, and only occasionally). The oil light flickers at idle when the engine is fully warm, but it NEVER stalls. I mean, everything runs perfect, and there is no loss of power steering or anything at idle. But it isn't where it should be. Plus there is no increase in RPMs when the a/c goes on; the RPMs momentarily dip then recover to 600-650.

Here is what I have tried: new TPS, new IAC, throttle body and every vacuum hose I could find checked (all clear and clean), crankcase ventilation checked (clear and open), throttle body cleaned and TPS adjusted (1/4 turn off the stop - should it be more - some one told me 3/4?)...I have a new O2 sensor but have a feeling that if that weren't working the car would not be running as well as it is.

Maybe my tach is faulty. How can I check that?

Anyone have any possible solutions? Being the perfectionist I am I can't let this go.

BTW the problem I was having with oil leaking and big plumes of smoke behind me after boost seems to have been, of all things, the cam cover gasket. I still want to check the turbo oil return pipe to make sure it is open and clean.
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Darius in Albany NY '86 744 GLE, '91 745T