What sensor controls the engine RPM when starting cold?

What is your question?

When the engine is first started (cold), the engine goes to 2,500 RPM. Once the engine reaches operating temperature the idle is normal. The engine runs great with no problems. What sensor controls the engine RPM when starting while the engine is cold?

What makes this problem better or worse?

It only happens when the engine is cold.

How long has your 1991 Mazda 626 had this problem?

Around six months to a year.