1990 C4 Idle issues
 

Just purchased a 90 C4.
PPI stated needed new batery
Always starts fine and turns over well
When returning to idle dips down to >500 rpm and mostly recovers
On a couple of occasions about five minutes after starting it will die a few times when returning to idle.
Seems fine when fully warm
I also noticed the clock had lost time in the last couple of days - does it have a low voltage cut off?
Could this be a battery issue? Other thoughts??
Thanks
Sam