I need some advice on an idleing problem on my 1981 240 wagon.

Here is when the problem started:

After one year of siting and working on rewiring the engine compartment,

I gave up and let a repair shop finish the wiring (they did the section below the FI unit). The Idle is really high now that the car is running again. I don't have a tach, but I guess it is around 1500 to 2000 rpm. As soon as I put it into gear it drops down so far that it almost wants to stall out. The mechanic at the garage says he thinks it may be the IAC motor??? I've already given them enough money already. I've got to do this myself now.

Is this the sensor bolted to the top of the valve cover with the large vacuum hose under it? The car has been setting for over a year. Is it possible that the trans or torque converter is gummed up from sitting. The car has almost a quarter million miles on it, other than fluid changes, the automatic trans has never been worked on. Am I looking in the wrong direction? Is this an electronic problem? I've got to figure this out or else I night break a U-Joint puting it in gear.

Ben