2006 Idle speed increases

This started happening sometime in the last year. I will be setting at a red light or anywhere at a stop with Jetta idling around 800 rpm. suddenly for no reason the idle will jump up to over 1000 and stay there.
Any ideas?

Probably the battery is low on charge, or a load on the system, requiring the engine to turn the alternator faster in order to compensate and provide enough electricity. Might as well clean the grounds in the engine bay. Mine used to do it too, randomly. Since I have replaced the battery 2 months ago I have not experienced a spike in RPM.

Thanks, I'll do that right away----

Also if the coolant temp sensor is sending a wrong signal, and the ECU suddenly thinks the coolant is super cold, it could cause the idle speed to increase (like a cold fast idle).

I'm experiencing a similar somehow issue. I've noticed that my idle speed has gone from the 850+ RPMs to the 950+ RPMs (warm engine). No idea what could be the reason. Input would be greatly appreciated.

I’ve seen a failed alternator pulley cause this.