Just wanted to share this problem.

1991 940 turbo with 182,000 miles.

Started off as a little stumble as soon as I let off the gas at highway speed. I could see the tac drop 100-200 rpms, no check engine light.
Then the car started to idle erratically after coming to a stop light. It would never completely stall.
Cold starting was fine. Starting after hot would sometimes require pressing the gas pedal.
Later the car stumbled a lot even at lower speeds.

I cleaned the IACV (Idle air control valve), but still had the deceleration stumble.
I was going to clean the throttle body, but I had done it 2 years ago along with replacing the main fuel pump, and the fuel pressure regulator.

Just to be sure I removed the vacuum hose from the front of the fuel pressure regulator and gas poured out of the vacuum line! The regulator went bad after only two years. I bought a Bosch fuel regulator from a local import dealer for $72 and the car idled and ran beautiful after.

///ed///

Thanks for the post. It is great when you can post what the problem and the solution was. It helps the other guys when they experience the same thing. You get an official Volvo-Forums ATTABOY!