I did a search, but I couldn't find anything with the same problem. I installed a PFC about 8 months ago. It went through the whole idle hunting part and it leveled off about 3 weeks later. About two weeks ago the idle has been doing weird stuff again. Whene I start it, it will shoot up to 2500 rpm then fall off to 1200. If I use the accelerater then idle it will start bobbing from 1000 to 1500 rpm like it is searching for idle again. If it sits for about two minutes it will stop, but it is still high. It has no problem with rpms dropping to low. My mods are just the PFC, intake, CB, and radiator. Someone said it might have to do with the plugs, but I just changed them 5k mile ago. Any help please.

 

Mine is doing the EXACT same thing. I'm getting tuned by Steve Kan on Oct 3rd, hopefully he'll be able to fix it. I have a new motor with new plugs that are only 3000 miles old, and it just started doing it when I installed the PFC, so I know it isn't the plugs. I'll let ya know if Dr. Kan can fix it.

 

911GT2

Your car is supposed to hunt for idle for a while after you instal your PFC. If you just put it in, it should do it for at least two weeks, ive heard. Mine did it for about a month. Every day it was less and less. This is 8 months after installing it. And mine was running fine for a long time.

 

Check the ISC Guys. It was My problem that I hunted for a long time. Unplug it while it is bouncing and see if it stops.

 

Mine has been doing it for at least a month, and continues to do so now. I'm hoping the tuning will fix it.

sub-zero ISC= Idle stepper control? Where is it?

 

ISC is Idle Speed Control. It's located behind the UIM, by the elbow. It's labeled the Idle Air Control Valve in the service manual (section F).

 

on the vaccum hose routing diagram I found an air control valve, but its underneath the UIM. Is there something else labled IDLE air conrol valve that im missing? Thanks for the help.

 

its on the back side of the uim(near the fire wall) with a white plug.

 

I unplugged the idle speed control and now it is fine. Can I leave it unplugged? Will it hurt anything or do I have to replace it. Thanks again

 

Or is the ISC something you dont need with the PFC?

 

JPJ- mine is doing the same thing... can you snap a pick of the iac? I don't have a service manual.... thanks..

 

I cant take a picture, but the best I can tell you is that it is on the back side of the throttle body. Its actually connected to the throttle body, not the fire wall. Its also the only white plug on the back side there. Its a little hard to get to.