I've been trying to solve an intermittent idle problem on my '90 740 turbo (155k), to no avail.

The problem:
The car generally idles well enough, but occasionally, while in drive and having just stopped the car, the idle slows down to 250 or so, and then back up to normal (approx 700-750). The tach needle then swings up and down between these two speeds for 5 or 6 seconds before settling back into normal. The car does not stall (I've been assuming that the computer is working to prevent a stall).

A typical time that the problem will occur, is when approaching a stop sign at the top of a hill, meaning that I am under acceleration, and I then let off the gas. At it's worse, the dash indicator lights may beging to flicker, most times they do not.

The problem does not occur consistently.

During the last month, I've been under the hood quite a bit, first successfully fixing a hesitation problem (a bad idle air control was the culprit), and have replaced a number of components and performed various maintainance in search of a fix for the elusive idle swing. I've not minded spending a few bucks on parts, as I want to drive this car for another 100k, but I am getting stumped (and increasingly broke).

Here is what has been done this month:

- New plugs/wires/cap/rotor.
- New air/fuel filter.
- Cleaned/adjusted the throttle housing/valve.
- Replaced all vacuum hoses (not Volvo hose, but the fit seems to be okay).
- Removed and cleaned the inlets where Vacuum hoses connect to intake manifold.
- New Fuel Pressure Regulator.
- New Knock Sensor.
- New Oxygen Sensor
- New Air Idle Cotrol Valve.
- Checked for Injector seal leakage (by spritzing water)
- Sprayed contact cleaner on Air Mass Meter Electrical Connector.
- Visual inspection of the Air Mass Meter's innards (it appeared to be clean and intact).
- Cleaned the PCV Tee (where flame trap would be on a non-turbo).

Within the past year, the car has also received a new main fuel pump, and (unfortunately), a new head gasket (at which point I had a new timing belt installled).

The only parts left to replace that I can think of are the Cold Start Temp Sensor and the Air Mass Meter.

I've also not replced the big hose that connects from the PCV Oil Tee to the rubber hose near the turbo. It does not appear to be cracked, but is rather hard.

Could this be a bad Air Mass Meter? Other than this flucuation, the car runs fine: no "limp home mode." I hate to buy this part if I don't need one.

Help me please! I can't figure this out.

Thanks.