I’ve got a 2011 mustang GT with a boss 302 and a live wire sct tune (tuned by a performance shop) and I’m having issues when I’m in neutral the RPM’s will sure up and down and the car will eventually die on itself! Need help!

 

that is a pretty common thing but I'm not sure of the exact cure . . . first clean everything (throttle body, MAF sensor, ...) and then it might be good to try the "idle relearn" procedure: disconnect the battery for at least 10 minutes; then with the engine cold, start it and let it idle while it warms up; then turn on the A/C and let it idle with A/C for a while . . . I am not sure of the exact timing for all this, but I think it's something like 5 minutes without A/C and then another 5 with A/C on

 

What bert said. It could be the MAF sensor. Kine did the same for a little while. I cleaned all of what bert said and then did the relearn and poof it was gone. Hope it helps

 

Bert is spot on. Check the owners manual. There is a process as he pointed out that will train the car to idle properly.

Here is a screenshot...