I have a 1987 k5 350 motor is brand new crate motor with no mods. My problem is the motor hunts when started idle goes from say 600rpm to 1500rpm then to almost 200rpm almost like its gonna stall? once the truck is placed in gear it stops. Sometimes when its started it will not do it its totally random doesnt matter what the weather is etc. I so far have changed the computer, tbi,idle air,temp sensor,egr valve and a new cat..the problem was present when the old motor was in it.