I apologize for the what may seem like monotonous info but I feel as if its important to mention... Lito and I have been battling a return to idle issues for quite some time. Before I go on a rant I suppose, I want to mention some things to get your minds flowing. I noticed this issue start to get worse when im parked at an incline for a few minutes. Id start the car back up and it would run rich (afrs dropping to 10-11s rich) and when I did my bbk longtubes I replaced an o2 sensor with a bosch sensor (not the cheap one) Maybe I should get an OEM one? I dont think the o2 sensor matters but FWIW....also I pulled the vacuum line off the fuel rail pressure regulator and if i plug one side of my nose and sniff I smell fuel so I'm going to go on a limb and say its bad and has just been getting worse over time and it would make sense for the car to run rich after sitting at an incline because the fuel going into the vacuum line...ok heres my mustang info .... 2008 Mustang GT Manual. Im full bolt on with hot rod cams, offroad prochamber, jlt series 3 cai, new motorcraft spark plugs, msd blaster coils, ford racing intake manifold, bbk longtube headers and ford performance twin 62 mm throttle body and a jlt catch can on the drivers side. Earlier this week I had an issue with my tps sensor and threw code p2135 replaced the sensor and figured i'd upgrade the throttle body instead of going stock i went with the twin 62 mm ford performance TB Before I did replace the TB, I still had some return to idle issues. I datalogged tonight for lito and went through two tunes and he is working on another one tomorrow. I hate to bombard his email with things im finding but it just so happens that I find something else right after I send an email. So for starters, I get some idle surging in neutral when coasting to a stop and when i stop it drops to 500 then back up to 1000+ and back down and returns to idle. If I rev in neutral it does the same thing. Past tunes have done this (besides the surging in neutral). I can post datalogs as well if somoene wants to take a look..