My 940 misfires on acceleration and even at idle when cold. As the car warms up, the idle settles down, but the serious misfiring continues on acceleration. When cruising all is well. But as soon as I try to give it some gas it misfires. This continues for about forty minutes, long after the car has warmed to operating temperature..

And then? It ceases its misfiring and runs as well as it ever has run, smoothly going up through the gear changes [it is an automatic transmission] and in general acting like its old self.

I checked the distributor cap for oil and did find a little on the rim which I cleaned off. The cap is not a new one and the rotor looked a little rough around the contact edge when I removed it and looked at its condition. I cleaned up the rotor contact edge and did a little sanding at the contact points of the cap but when I took the car out later it returned to its misfiring.

Anybody else experienced this?

Bob