I have a 2006 Mustang GT and the JLT II/X-2 with canned tunes which worked great with the initial install.

Last year, I changed a parameter (fuel economy to normal) and I got the RPM problem (RPMs fluctuates up and down sometimes below 500 and stalls, especially when coming to a stop). I had to take it to the Ford service center to reset the computer back to stock (with the stock intake re-installed). Re-installed the JLT II/X-2 canned tune and everything was great again.

Now I changed another parameter (91 octane tune to 93 octane tune) and the same RPM problem surfaces!

Why can't I just change a parameter on the X-2 anytime without this problem? Isn't the X-2 designed to change a parameter any time I want? Is there a way to erase the adaptive memory myself? (disconnecting the battery didn't work for me)

 

Hey man, I KNOW what you're saying as I've experienced the same problem time and again. Try cleaning your throttle body. There was a long going thread of people w/ similar problems who cleaned the TB and had the problem cease. I just bought a bottle of TB cleaner, but have been too lazy so far to get to work on it.

 

I change between Dougs 91 torque and 93 race all the time and never have any problems

 

i'm sure it's just a coincident..
dirty throttle body by the sound of it (i struggled with mine for 4 months going after all the symptoms i thought were related, till i realized all it needed was a scrub with a toothbrush and WD40!)