I have a 1990 IROC-Z with a 5.7 and a T56. My question is when I come to a stop my car is idling really high. If I rev it up high it will settle down and then be fine. It seems to mostly do this after the car is warmed up. Do I need a t5 manual ecm or prom to fix this? It also has a 160 degree thermostat that the previous owner put into it. Could that be causing it? Lastly it basically has no emmisions or cat and the mufler comes right off of the y-pipe. Could lack of back pressure also maybe be causing this? Thanks in advance!