High Idle issues with new 2010 6.4L

[dc4]

I traded in my 08 6.4L for a 2010. On my 08 when I did the high idle mod I used a transistor to achieve 1320 rpms. Well on my new 2010 I used a potentiameter. After instal and a test the engine light lit up so i shut off the engine and started it back up. This time the engine light went off but the wrench light lit up so I shut it off again and restarted it, this time I had no warning lights come on. However after using it for a couple of days I have noticed that when I turn the High idle on the rpms vary plus or minus 200 rpms. This bothers me a little bit because on my last 6.4 when I hit the high idle the rpms were steady. Could I be using the wrong potentiameter or possibly crossed some wires accidently while installing it. Thanks for any help guys.