IM waiting at a light and all of a sudden the car idles rough and then it cuts off, then i try to restart and it takes a while to turn over. Also i step on the gas at times and nothing happens the car is just idleing rough. I have a 1996 5 speed i30t with intake y-pipe and cat-back exhaust.

 

Looks like the AIC valve might be getting dirty. Really hard to tell over the internet. This assumes your car is in good working condition already(ie.. no error codes, recent tune-up, pcv valve is in good working order etc.......)

 

sounds like your Throttle Body is dirty.. i had this problem.. it would idle rough and when i come to a stop the idle would dip below 500 and come back up..

I cleaned the Throttle body this weekend and the problem has not come back!!!

i got the TB cleaner for Fuel Injected Engines from my local autoparts store..

you should check this first.. about 15 people in this forum have been through this and fixed their problem this way