The alternator would not cause a problem. Your fuel injection is entirely mechanical. It's probably just coincidence that this occurred at the same time. I would look more to a fuel filter probably needing replacement.

On the other hand, how long was your car down? It may just need a little running to get a few of the cobwebs out. Altering the idle speed would only mask what the real problem is, and usually only temporarily.

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )