high idle

my 93 rt tt is idleing very badly.....but it only idles badly every once in a while...what could be the problem...the rpm sits at about 2.5K...it does this even after the car is already warmed up....also my car dies every once and a while...i start it up, the engine struggles and then the rpm falls and the car dies....what could be the problem???

Could be in need of new plugs, could have vacuum leaks, or it could need new o2 sensors.

Could be dirty throttle body/idle controll valve also, if you havent allready you should do a pressure test on the intake and clean out the throttle body while your at it.