Question number 1 Is it possible to have a 740 (with 8 valve engine) that actually idles?

I have read and read the FAQ and done everything I can think of.

Cleaned throttle body, cleaned flame trap, cleaned all hoses and vacuum ports. I took off the breather assembly on the crankcase and cleaned it. I have reset the throttle plate, cleaned the idle control valve. I have used a spray all over the intake system to look for vacuum leaks. Still it hunts...but not all the time. Sometimes it steadies out. If I engage drive or reverse it steadies.
If I rev it in neutral it revs high then hesitates a bit at about 12-1300 rpm then goes down to 600. Sounds like a vacuum leak but I can find none. When it is steady, I see about 20" on the vacuum gauge.
Its driving me nuts and from what I can read, I am not alone. I am beginning to think there is no such thing as a Volvo that will idle correctly.
Car drives great, good power and driveability.

What is there left to try ?

Question number 2. I have a Regina system (1990 model). Where is the ECU located?

Question number 3 I have removed some plugs under the hood (relays in front of coolant reservoir) and there is a brown glue or whatever holding wires into the gray plastic plugs. This amber looking stuff disintegrates and the wires stay in place on the socket pins when the plugs are removed. Is there a trick to hold these plugs together again?

Thanks for any words of wisedom.

Steve