Hi, my 85 740 B230F has a hitch when it gets humid and/or cold out...
The Tach sits there lifeless even with the engine running for about the first 10 mins. of driving. Eventually it catches up and matches engine speed perfectly... as well, the car has problems idling and hesitates under 2000 RPM. Over that it roars like a demon and drives fine.
in the past few days I've checked and ruled out:
-the F.I. relay
- the fuel pumps
- the knock sensor
- the power stage
- the coil/cap/wires
- dirty connections
the following appear to be working/not malfunctioning:
-the AMM
-the FPR
- vacum lines
- the Throttle Pos Switch ( clicks properly)
- the IAC ( checked it 1 month ago, nice and clean inside)

I'm pretty sure there are no air leaks, although I might redo the injector seals as the injectors turn in their mountings a little too easily for my likeing.One strange thing, is when I unplug the ECT as the car runs, this sucking noise appears, then dissapears when it's plugged back in...strange.
Like I said up top, the car Roars! in the higher RPM (2000 and up) but below that it hesitates, stumbles and all that good stuff.
The Hall Sensor mountings on the Distributor are solid, though I haven't broke out the ol'multimeter to test it...Usually it gives grief when the car has warmed up, right?
The advice is ALWAYS appreciated! Josh