I first brought up this problem a couple of months ago and haven't solved it yet. The car is a 1992 740 wagon.

http://www.brickboard.com/RWD/volvo/1315160/740/760/780/wont_rev_restarting.html

This only happens in cool or cold weather. I thought it was an intermittent thing, but it apparently isn't. To recap, what happens is that when I restart the car while the engine is still warm and start to drive off, the revs drop to a slow, erratic idle within less than half a minute. This usually happens when I've pulled out of a parking space, so there I am, barely moving, holding up traffic. The throttle is completely unresponsive, except if I give it too much gas, it might die, but always restarts okay. All I can do is wait it out for a couple of minutes and the revs climb over 1000, then settle down to normal and all is well. Last time this happened I heard a backfire in the intake while pumping the gas, so it almost seems like it wasn't getting enough fuel. Although this is not a debilitating problem, it's annoying as hell and I'd like to get to the bottom of it. Otherwise the car starts instantly every time in all kinds of weather. and when driving I've never experienced anything that would indicate the fuel pump wasn't working.