I need some help narrowing down what the issue is...

Today my throttle servo got stuck in WOT while practicing before the race. I initially assumed the receiver pack was dead but it was not so I swapped out receivers and also put in a fresh pack. I didn't have any more issues until I started it up again for the main. Everything was working fine until the engine actually fired, than the servo would go to WOT. As soon as the engine was stopped, it would work fine again. I tried 3 or 4 times with the same result each time.

Since I changed receivers, I assume its not the receiver. It did happen with the same battery both times, but the voltage was fine and the last time it was fully charged. So that would leave either the servo, which is only a month old, or the transmitter??

I'm using a Airtronics M11x, Futaba BLS157hv powered by a Protek 2300 lipo.

Also, I do have fail safe settings set up on the radio.

Seems like either a switch or servo issue. try plugging the batt diewctly into the rx. If that doesnt fix it, try plugging in a new or known to be good servo and fire it up.