I have a 1998 Chevrolet Prizm that will not fast idle when it is started in cold weather the first thing in morning. what could be the problem?

Mileage? Is the check engine light on?

It could have a dirty throttle plate, but since the advent of electronic fuel injection, I didn’t think cars were supposed to do that anymore.

I’d suspect the temp sensor. I’d suspect that the ECU doesn’t know the engine is cold.

You may not even get a fault code with this, because the ECU may not know the engine is actually cold.

Can you be specific about exactly what the car does when you start it cold? Include the actual RPMs.