1994 Cadillac EL Dorado whats wrong

My cadillac was park for 3 month it was running fin when I parked it. When I got it back out it started acting up. When you first get in it of a morning it runs fin then when you drive it for about 3 miles it starts surgeing rilley bad then when you pull up to a stop light it will surge and then stall. While its surgeing going down the road you can speed up and it will do fine but when you let off it it goes back to surgeing