Well heres my issue. Sitting still the throttle will go from regular idle, to 1500rpm, and the up to 3000rpm. Then I will rev the engine higher and it will go back to regular idle. What is causing this. It has almost caused accidents, and i need to get this fixed?

As well the A/C at random speeds will blow cold, then hot, then cold. It also varies in force while being on one setting? Also as well the headlights and cluster lights flicker like a spike in voltage, when above 50 mph. If anyone can help me on this i would appreciate it. Its in the shop today, but they said they fixed the problem, and it still acted up last night.