Recently rebuilt engine with PFC on first 500mi oil change. I changed the oil, warmed it up, took it for a quick spin to the store and back. Everything is fine until I get to my driveway, where the idle starts bouncing between about 950 and 1400rpm continuously. Sounds like I'm sitting there blipping the throttle. Very regular and rythmic. Took it back out and it just does that all the time now. Bounces and never learns or settles down. The car seems otherwise totally normal and drives fine. If I turn on the AC the car settles into a high but steady idle around 1300rpm.

Previously the car would hunt for idle a bit when cold and stalled once or twice when clutching in at a stop (again, only when cold), but had a steady 1k idle when warm.

Looks from searching like I need to look at the idle control screw and the TPS, but it seems weird when this problem appeared so suddenly. There couldn't be abything about changing the oil that could relate to this issue, right?

 

Check all of you wiring/hoses around the oil filter. You likely knocked something out of place. A properly done oil change will have no effect on idle.