car is jerking and shaking

[skylarkgs]

hi everyone im new to the whole forum thing and was reading some of the information you guys put out there and it was very usefull.i have a 1996 buick skylark gs 3.1 and ive noticed that it seems like its about to die(jerks forward at lights or when stoped and then goes away)i dont know the history of the car so ive changed plugs and wires ,fule filter and got my gas lines and injectors cleaned at the gm dealership,anyone have this problem and i m not shure if it s a tranny or engine becouse it doesnt do it when in park

[gpse3400]

Might be IAC(Idle Air Control) motor malfunctioning. Might just need a good cleaning. Does it run smooth regardless?