What part is failing when the engine speeds up and slow down then repeats?

What is your question?

This happened when I started the car this morning. Upon starting, the engine races to 2500 rpm then slows down to 500 rpm then this cycle repeats. I did not drive the car this way. The 'check engine light' did come on the previous evening but was not on this morning. Obviously, I hesitate to drive the car this way.

How long has your 2004 Pontiac Vibe had this problem?

Just started