i dunno how your car is setup, can u turn the controller and control the servos without having the motor running? if so do it, make sure the throttle servo spins both ways the way its supposed to. if its ok then check if it works under pressure. or u can have then engine running, hold the car in the air and watch if the servo functions correctly.

when u apply the brakes do the brakes actually work or is the command just ignored?