Hello,
my daily dirver is a 1988 745 with a B230f non turbo engine. The car has covered 334,??? k and a part from piston slap when very cold, it is really very good. Compression is even and high on all 4, does not burn oil, petrol consumption is normal at 23 Ml/G. In the last 2000 k I cleaned the TB, the idle stabilizer, the injectors, replaced the O rings, changed the timing belt and all 3 front seals, plugs, filters and cleaned all grounds. New oxigen sensor. I even replaced the head liner and converted the AC to 134A. It has a Bosch 2.2 lh system and a auto AW trany, also just serviced along with the rear axel. This is a good car.

HOWEVER, on occasion the minimum RPM refuses to go below 1100 to its normal 700 RPM with gear engaged, and 1500 when in park. Even then the car works well, and stars easly, does not hesitate and still climbs up an other 200 RPM when the AC is engaged. This never happens when cold, it may be related to heat soke but it is not consistent, there are no vacuum leaks, not even at the intake, used a stetoscope for that test as well. In addition, on 4 or 5 occasions the RPM counter needle swang wildly up and down several times, only to return to normal beahvior. THoughout the car did not miss a beat. The Hall sensor test OK.

WHAT SAY YOU? Thanks, Andrea

In additon to Rob's suggestion, test the throttle position switch functions per 700/900 FAQ instructions: if this fails, the ECU does not realize the throttle is calling for "idle" and does not activate the IAC valve.

While it really sounds like a vacuum leak to me, I would consider replacing the idle air control valve. That's the silver canister under the intake manifold with 2 3/4-inch rubber hoses and a plug going to it.
Get one from any 85-88 240 or NA 740. Ought to be a good junkyard item for $10-20. I'd just plug it in and try it, see if that makes any difference.

If not, I'd definitely go over that intake again, spraying WD40 or carb cleaner onto all the seals. See if anything makes the idle change that way. If so, that's a leak.

Good luck!
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Rob Bareiss, New London CT ::: Roterande Fläkt Och Drivremmar!