Irregular up/down revving ('92 Seville)
 

Hello, first post here. Thank you for having me.

I inherited my dad's '92 Seville and I like it a lot. Very strong car. The main issue it's having is irregular revving when idling. It goes waaayyy up, then back down to normal, then back uuup, then back down. Sometimes after a bit of driving it'll settle down and remain normal, but not always. So now I put it in neutral at stoplights, so it's not straining against the brakes as it revs.

I looked up some posts with similar issues. It seems maybe I could 1) change throttle position sensor, 2) change the idle control valve sensor, or 3) clean the throttle body. If anybody has any other ideas, I'd love to know!

One other thing: I got the car back from a mechanic a while ago (fixing different issue) and found a part lying on the side. I wonder if this is what is causing the problem. It might have been around the time the revving started. Here is a picture:

https://cimg0.ibsrv.net/gimg/www.cad...33d3647c29.jpg