When the car is warmed up and I come to stop, with the clutch in or in neutral, my idle will go down to about 800 RPM and then zoom up to 1500 RPM and back down to 800 repeating the cycle.

It does it about 20% of the time when I come to a stop.

The car was recently in for some cosmetic body work (new hood, left front fender and left headlight cover). I talked to the body shop and they claim they didn't touch anything with the engine.

Any ideas?

 

There is a switch on the transmission that tells the PCM that the car is in neutral.
If this switch fails (and, apearently, they are failing in some significant number), the PCM never knows it is in neutral and doesn't go into the idle loop.

Attached are the relevant wiring diagrams.

 

Here is the diagnostic routine.

 

MazdaManiac (Jeff),

Thanks for the detailed info, very helpful.

It sounds like it could be the switch or the PCM. Before I take it into the dealer, should I remove the Canzoomer unit or is it not necessary?