Hello, I am from Guatemala this is my first post, I want to congrats to everyone for the good information that was rery helpful to me.
I want to expose my problem, maybe someone has a similar.

My car it is a 2005 Mustang gt, when I release the gas pedal, the engine continues for several seconds in the same rpm's and then very slowly goes down. I clean the throttle body, the probem continues, I have the diablo predador and test some configurations and even return to the original factory the problem continues.

I only have cold/air induction K&N and Long tube headers HOOKER every help will be grateful.

I had replace my gear to 4.10 and my 1/4 times got worse.
I want to return to the original but I don't have the original factory measures calibrations, where can I found it?

thank you.

 

check the tune for the cold air intake and the 4:10 gears. maybe thats giving you your idle problem

 

If you reinstall your factory tune and the problem remains, then likely the problem is not tune related however I don't know if the headers/intake would cause that problem for some reason. As easy as it is to change intakes, I would reinstall the factory tune and intake and see what happens.

As far as 4.10s impacting your ET negatively, likely its because you can't get traction. I know in my situation, with 4.10s and factory wheels/tires I spin all the way into 3rd if I don't baby it.

 

Take it into the dealership but return to original and remove the k and n to have them check under warranty, the problem could be anything in the drive line, even though to me it sounds like a bad throttle body or mass air flow censor