It has no codes, nothing.

The fluctuation is so rhythmic, Its like when the tcm tells the ecm to drop rpms for a shift, but no shift happens. Up down up down up down up down by several hundred rpm about once per second. But I already ran it in manual with tcm disconnected and it still happened. It happens with everything disconneted, except the coolant temp sensor, thats the only one I havent tried unplugging yet.

My egr wasnt dirty, but the port in the common chamber was totally crudded over, so I cleaned all that up. I think that gave me an egr and lean O2 code before all this started, but its fixed now.

The intermittent airbag light is about the only clue now that something unusual electrical is going on.

Can they test an alt on a vehicle? That beats pulling it.