Good to know you have the tethered DC motors with "var". Since you didn't list wireless Bits or the BLE Bit, is it ok if we refer to your project as autonomous car or programmable car instead of remote control car? Along that line of thinking, below is a project to inspire you.
http://littlebits.cc/projects/autocatch by Tuna Tumer
Below are the analogWrite statements Tuna uses to make a tethered DC motor (switched on either CW or CCW) go forward and stop in intervals. When placed inside the void loop, these same lines of code will cause the tethered motor to go forward and backward if the micro-switch is set to "Var".
analogWrite(9,255); // 9 is the pin. 255 is the highest analogWrite value, which is equivalent to a slide dimmer in the rightmost position
delay(100); // wait 100 milliseconds
analogWrite(9,0); // 9 is the pin, 0 is equivalent to a slide dimmer in the leftmost position
delay(1000); // wait 100 milliseconds
More info on analogWrite:
Please feel free to reply to this thread with pics of your circuit and snippets of code as you go along. Other Bitsters will likely chime in with helpful input and maybe even a little debugging.