I just got a 1991 Pontiac firebird from my father and it’s a 3.1lv6 with a manual transmission and it has a strange issue I can’t figure out when I’m going to downshift or when I just push in the clutch to come to a stop the rpm’s go up considerably high then peg out at a certain rpm I can’t remember and then they won’t go down until I’m almost completely stopped is there any fix for this?

 

First thing I'd do is check for a sticky throttle, try actuating it by hand and make sure the throttle body closes completely and immediately once you let go.