i just put a new radiator in today nd after i was done filled it up and turned it on the car started fine but after it started to warm up the idle would go up and idle high for like 4 seconds and drop down almost killing the car and after a while it stopped so what happened was that bad.any help would be great.

 

not a problem - what happens is that the water temperature sensor for the ecu is at the top of the motor (sometimes higher than the radiator) and if you have a small air lock in the system, the coolant doesn't reach the sensor so the ecu thinks it is still cold and sends more fuel - when the engine speeds up, some of the coolant bubbles up to the sensor and the ecu reacts - make sure you are completely filled with coolant - i don't know about all of the motors, but a lot have an air bleed valve on top of the thermostat housing that you need to open to make sure all the air is out.