My daughter has a '91 Seville FWD with only 54,000 miles on it. She was away for 4 weeks and it sat unused. She has driven it for a couple of days and it is idling inconsistantly - sometimes at about 700 rpm and then bursting to 1600. She says it is running rough as well. Before she left it was fine.
It has a full tank of gas that I'm worried has some water in it. Other than that, does anyone have any ideas?
Many thanks.

 

I can't see water in the gas causing high revs, I'm thinking more like plugged EGR port or some such thing.Have you tried pulling any codes to get you started in the right direction?? Fuel filter been changed in the past year or two??