I just installed a 383 in my 90Iroc w/24# injectors, ASM longtube runners and numerous other mods along with a custom burned chip that was supposed to take all the mods into account. Upon start up, the engine ran up to 4000 rpm before settling down to 3500 rpm (my foot never touched the gas). It ran for about 10 seconds like that before I cut it off so that I could figure out what was going on. I checked for obvious stuff like kinked throttle cable or unplugged sensors, etc. but couldn't find any reason. The throttle plates were all the way shut on the idle adjustment screw on the throttle body. I figure I must be missing something real obvious but still can't figure it out. By the way I did hand prime the oil system before start up. Any ideas?

Thanks, Bill

 

Could be a vacuum leak(s).

 

did you ever figure out what the issue was with your high idle? i have a similar issue and am in quite a rut.

 

if you dont have any vac. leaks i would suspect the iac motor, it ranges from closed 10-to open 200, if may be difficult to see this with out a scan tool but it would something good to look at, the easiest thing may be to cover the iac hole, then start it to see what it does then, let me know what you find, happy motoring, thank you dr. engine

 

aaah, sounds like ill have some fun this weekend, i just found out that 3.1L engines do not reset their IAC upon start up like other engines so i guess its going to be fun finding where the computer thinks it is at lol

 

a easy temporary diagnostic test would be to remove the iac and cover the hole with a piece of duct tape(not allowing it to let any extra air through the throttle body) it may be a little hard to start that way, but when it does start i shouldnt peg at 4 grand, just a cheap test i thought i would put out there,