There are many systems working in harmony to develop a smooth reliable idle. The systems are numerous. Since you are most likely not a tech who is going to be doing the repairs yourself, I will try to reply to you as if you will be speaking to your service advisor or technician about the problems.
The idle surge should cause a “check engine” light to illuminate on the dash panel of your car. If so you are in luck! The repair technician can retrieve the code stored in the Diagnostic Module. After retrieval, the technician should perform diagnostic work to find the exact cause of your complaint. There could be many codes in a series, but only usually only one caused the complaint and the “check engine” light illumination.
Some causes that I have seen are as follows: 1. The self-adaptation is at its limit. This means the engine is running too rich or lean. IE air leaks or faulty sensors. 2. The engine wiring harness is cracked. See the bulletin board for more details on this. 3. A broken throttle return spring 4. A faulty throttle actuator
I hope I have helped!