I have a 1987 944S that I drive ocassionally like 3 times a week. I just noticed that today when I was driving it, the volt meter dropped from around 13 and slowly dropped down to 11 while I was driving. Started to get a little worried but after maybe 5-7 minutes of driving, it started to creap back up to 12 and just slightly past that and stayed there for the next 5 minutes or so.

When I drove the car home, it started around 11.5 and slowly went up to just past the 12. Is this a sign that my alternator is going bad?

 

Check the alternator belt tension.
In a dark garage, car at idle, does the dash light just barely want to flicker?
How old is your ballery? Using the car 3X a week may not fully charge the battery with short trips. The battery charge memory could cause problems if 4 or 5 YO.

Clean the batt cable connections.
Clean the big NEG ground connection on bell housing. Put a piece of tape over the TDC hole!

Take car to LAPS (local auto parts store).
Take out alternator and take to LAPS.

Pull the VR and check the brushes. They should be 1/4" to 5/16" long. If not, replace after you sand, clean and polish the internal slip ring to avoid chewing up the new brushes on old groves.

After you do this and spend a few hours and no change, its the alternator. A diode going bad.

I replaced my OEM 90amp with a 115amp because of old battery cables (more resistance), wires, fuel pump ++++.

GL
John_AZ

 

I had this happen to me when the belt was not tight