Problems with 96 Pontiac Firebird

hey all i recently bought this car a few weeks ago with 100,000 miles on it.....got it looked at the other day mechanics said nothing big was wrong with it and that it just need some of the fluids changed or flushed...also the front brakes needed to be replaced.....so i got all that done and took my car to wash it today and as soon as i was done washing it i turned the car back on and it started chugging as soon as the car got to a certain rpms and the engine light went on as well.....i need to know whats wrong if any u all could please help me.....i want to get it fixed asap....also i was wondering if i should be driving it still b/c i wasnt planning on it until i take it to get it fixed