The same thing happened with my Tornado when I took it all apart to get a better idea how it works, and every single time you disconnect the throttle horn. Its an easy fix.
Turn on your remote and your car's electronics with the servo horn off. The servos should return to thier center positions. Pop the servo horn on so that the carb is as far closed as it could be. Screw it all back in (don't forget the brakes!). You might need to mess with the little throttle trim dial on your remote to get it perfect. You can also do the same to your steering servo.
Please tell me if I have posted an incoherent or irrelevant answer!