I have a 91rs 305 tbi. I've replaced all sensors except map. It was just starting to run better when one day it had a backfire/throttle body spit. It has only gotten worse and also has a strange idle that misses every so often. However it runs much better after being driven for 20+ minutes. I just replaced the ignition coil and it still seems to have this problem. Any ideas?

 

plugs
wires
check timing
check fuel pressure