Throttle Unresponsive while rolling slow

[CELouroboros]

Hello, I have a 2012 Mustang GT and it has a problem with starting from a stand still. I narrowed it down to it happening while the car rolls extremely slow(like 1 to 3 mph) the rpms will raise a bit and hang but I won't have and throttle response. It constantly causes it to start rolling rough or stall unless you get it just right(and even then it's a toss up). It's a t56 magnum xl swap. My guess is it might have something to do with the wiring to it since the speedo jumps up to while this occurs. Even going to rolling really slow from already driving will cause it to have the issue(while the clutch it pressed in or in neutral) It is throwing a code for upstream 02 sensors which I have and am going to replace soon once I have time and can get those old pos one's free but I'm not sure if that could contribute to the cause at all. Any input or help is appreciated.

 

[86GT351]

Are you sure there are only O2 sensor codes? Have you checked the fuel trims while driving? Any data logging?

 

[Juice]

Did you make changes in the tune for the XL?

 

[CELouroboros]

Sorry for the late response. Last time I got it checked it only had the o2 code so unless something new popped up but even still it was having that issue when I first got the car(there was no CEL on for the first month or so I had it). Haven't data logged or checked fuel trims, I'll probably pick up a scan tool soon to do so.

I believe the previous owner said it was tuned.

 

[DamanC]

I have the same swap, I discovered too late that my wiring harness was resting against my long tube headers and was having the same speedo issue because my vss wire was cooked. I had to reroute the harness, replace a couple wires, and wrap the whole harness section in heat shielding. I haven't had the speedo issue since. I have had an idle issue but that may be from me messing up the transfer of the electronics to my new throttle body.