ahhhh, the horror stories of nitro. Best advice, take it to the track. For real. The guys and gals are more than willing to help out. They do at my track and to many others around my state that Ive been to.
My hyper 8 buggy done the same thing, it took off. Seeing 1000 dollar car run like a scalded dog towards a 4x4 post wasnt the best day in my nitro years. It turned out the servo gears stuck and wouldnt allow the throttle or fail safe unit to return it back to the preset possition.
Thats my story. And if I were you, try a hobby shop or your local track, most other racers are nice enough to help. Good luck.