Volvo: Chugging at idle 2, windsor ontario canada, new distributor cap

Question
Sorry Ray, I asked this question to Roger. But he needed more info and I could
not get back to him because he was "maxed out" on this list.
The question is:
have a 1990 Volvo 740 wagon GL model, 240,000 miles.
The car chugs at idle. Once it gets up to 15 -20 miles an hour, it's fine.
There appears no pattern, but it persists.
If the car is restarted, sometimes two or three times,
the problem goes away but may recur without notice.

Roger said he needed to know if the car has a regina system. It does.
And the car has had many parts replaced: oxygen sensor, fuel relays,
new fuel pump, air filter.
After installing a new distributor cap, the problem went away for a short time.
But it has returned. A new distributor cap of better quality was put on.
The problem went away for a day and half, but has returned.
It has baffled my Volvo auto tech who's a recognized expert in this city,
Windsor, Ontario, Canada.
He says we've done everything, changed everything and still no go.
So, he's going to swap out the two computers and see what happens.
He says if nothing else it will eliminate the computers as the problem source,
even if the problem recurs.
Ray, we're at our wit's end here. We replaced this regina system with a good,
used one several weeks ago, because the car was stalling as it was driving
along.
My Volvo tech believes it's electrical and could be some wonky electrical
connection that may be sensitive to outdoor temperatures. It's been well
above freezing here. Sorry for the long rambling note, appreciate any help or
clue you can provide, regards, Ted

Answer
Ted,
I would monitor the fuel pressure when this is happening. It should be 2.8 bar and rise slightly on acceleration. You may want to try a power stage and suppression relay also. I have seen more than one coil go bad also.
If your car has EGR make sure that the EGR is off at idle.