Does the issue happen when the car is at rest (ie on a car stand) or when driving it?
What type of esc and steering servo do you have, some high current servos can cause "brown outs" with the Spektrum receivers especially if the ESC can't supply enough power to the receiver.
I had a similar problem when testing a Savox servo hooked up to a Spektrum 3500 receiver, the cheap esc I was testing it with couldn't supply enough voltage and the receiver would shut down for a few seconds.
You may be having a similar problem to another person that posted in this section and might want to look at getting one of these
http://www.amainhobbies.com/product_...tage-Protector
Cheers
Rob.