I have a 2001 chevy prism (toyota corolla) that was having rough idle and miss problems only when the engine was cold. Once it warmed up to normal temperature it ran fine. A little background.I just put a new pcv valve, checked mass airflow sensor (it was new), new cat converter, new muffler, new o2sensors, ran 2 tanks of gas with fuel system cleaner, new plugs, checked all four coils, and checked to make sure the injectors were firing. Anyways. This lead me to the coolant temp sensor as the culprit that perhaps it was telling the computer the car was warmed up and not providing a cold start rich fuel mixture and advanced timing. A side note: the temp gague never read that it was overheating, it was always pinned up just under half mast. So once I changed the coolant temp sensor, I filled it with new coolant and held a funnel in the radiator to get any air out. Well here is the real problem. My wife was watching the temp gague and it read half way up from a cold start and then quickly spikled into the red within 2 minutes. So far as I know the thermostat was opened up and the car was not overheating ( it couldnt have been that quickly). What could it be. Is the new part faulty? Did it reveal another problem? HELP?