help- car stalls

[DLuded]

just imported a 89 gtst and at random times it runs really rough. by this i mean it will be running smooth and then all of a sudden it'll be as if im putting my foot to the floor then releasing it. it jerks back and forth every time i put my foot on the accerlerator. when i take my foot off it just rolls but once i put my foot back on the accelerator it does it again. it jerks back and forths pretty voilently...so i go to the side of the road and the car stalls. once i start it up again it rev at about 2,000rpm for about 30 seconds.

i was thinking it might be somehting with the fuel because it hadnt been started in about 5-10 months im guessing so all the sediment and crap in the fuel would have sunk to the bottom of the tank. when the car arrived the fuel was nealy empty and i drove it for about 5 minutes with this petrol. im thinking this may have cloged up some of the fuel system

also how do i check the engine diagnostic?

any thought?

[tridentt150v]

Water in the filter??