surging idle then stall
 

yesterday after about two hours of highway driving my 85 928S (5 Spd) stalled at a light when put into neutral to make the stop. It cranked right back up but was surging between 1500 and almost stall and I had to keep applying the gas to keep it running.
Several times I pulled over and it surged then stalled once stopped.
The car sat for about three months and the battery died which I replaced a few days ago. Had no issues with it that day or the two hour ride earlier in the day. It was the afternoon drive in higher air temps that seemed to bother it.
Any ideas why this would pop up now when it never happened before.

My first guess would be a vacuum leak somewhere. Does it idle OK from cold? Could also be the EGR (Exhaust Gas Recirc) valve. This valve sends exhaust gas back into the intake for reburning and the engine could be choking on its own exhaust at lower rpms.

Fine at cold temps -- seems like the EGR items might be the issue. Thank you