Simon1

I wonder if a faulty O2 sensor would do this? Maybe command more fuel as it reads incorrectly.

But I agree with unmetered air getting in, or metered air getting out. If the OP just worked on his ALT I would check the connections and make sure all is well.

Derf00

Maybe but a code would be thrown...something like a P0133, P0153 would be a slow to respond O2 sensor (Bank 1 or 2 respectively Sensor 1) that would cause that. As the car dumps fuel in, the O2 sensor responds too slowly so it overcorrects and the car cuts back faster than the O2 sensor responds so you get an effect similar to overcorrecting on a spin-out.