You have to start by a process of elimination.
Before starting up your motor switch on the receiver ONLY and see whether you get any glitching.
That will eliminate any local interference that might be causing the problem.

If that is fine then get the transmitter ON and the receiver ON as well. Any probs there?
If you ONLY get glitching when the engine is running then its a matter of poor screening from the high frequencies caused by the moving mechanical parts, and that is usually the receiver and antenna. Make sure that the receiver is well fixed with double sided tape and does not vibrate when the engine is running. Check also the crystal, remove it and make sure the sockets are clean.

You should also make sure that the antenna is not cut or being trapped under anything. Avoid coiling extra length from the antenna.

Hope this helps...!!