low vac. after minute long stop

[turbo buicks]

while sitting at a lite after about a minute the car goes from 11-12 vac. to 9 and gets real choppy. the SES lite also comes on when it does this. once i get going or put it in neutral it goes back to regular and the SES lite goes off. it only happens when stopped for over a minute or so.

any opinions???

 

[WarpSpeed]

What trouble code is it setting.?

 

[turbo buicks]

oops i forgot to mention i dont yet have a scantool