Rough running Saab fixed itself

Car was idling and driving real rough and dying at stops. Turns out that the transmission mount was torn so I replaced
it and verified that the other two motor mounts were good. Car was still running rough but on a drive with some jerky shifts (automatic) after about 20 miles all is well and I’m running as smooth as a baby’s bottom with great turbo action. Cars just don’t fix themselves. What could have been wrong? By the way there were no codes from the Tech ll. Using a pc of tubing I can’t hear any vacuum leaks nor when spraying brake cleaner on the hose ends does the engine race.

I don’t believe that the torn transmission mount and the rough running engine were related. I wonder if you picked up a tank of gasoline that was bad. It’s rare, but it has happened.

Saab 9-3
Model-Year ?

This is a 1999 2.0L turbo.
About two weeks prior to the rough running for no good reason other than annual maintence I added a container 6oz? of Gumout fuel injector cleaner to a full tank of gas and there were two weeks of good running after that pior to the rough running.
During the rough running I replaced the spark plugs with the proper NGK pulg gapped to the recommended 1.0mm. Prior to the rough running there was an O2 sensor resistance high code, so i replaced the 02 sensor with a new one. This did not immediately eliminate the rough running.