I started my car today and the idle was going up and down rythmatically till it warmed up and then smooth at 1000rpms. As I was driving around I noticed my idle staying at around 1250-1500 rpms staying smooth with no variations. I am running the fcon and my idle was bumped up to 900 with the cipher. I tried resetting the ecu and the idle stayed at 1250rpms but when I drove it around it bumped back up to 1500rpms. I can't get it back down to 900rpms. Does anyone know what is going on. I called the tuner who tuned the fcon and he doesn't know what is wrong. He said he'll make some calls and get back to me. Thanks, any advise is good advise- James

 

sounds like A vacuum leak. I am hunting down a similar problem.

idle hunts up and down.
idle won't go under 1000 rpm.
occasionally idle stumbling.
P0300 code (random cylinder misfire) at idle

 

Thanks I didn't think it was a vacuum leak because the idle is stable. It was only up and down once (initially). I reset the ecu and it still idles above 1200 rpms. I am going to have it torn down next month for a build so I guess I will leave it alone till then. I thought it was something to do with the ecu since idle adjustment is controlled by it. Well thanks- James

 

I just found my leak!!!

it turned out to be my home depot catch can was leaking air. I think I had searched everywhere else..... manifold on and off a couple times, all of my vacuum lines and accessories (alot of them).

Oh well, I just bypassed it for now.....I guess I need to find a nice catch can now.

 

Did that take care of your idle increase? Congrats on the find I will start my search tomorrow.

 

yup. my idle is back to about 900 with the A/C on. I had the idle bumped up with a cipher.

 

Sweet you have been really helpful and i thank you!!

 

your welcome! These forums are great fro solving problems!!!