I agree with Tom.

Check things one at a time after unplugging everything. Plug something in, if it works, great. Do this one at a time for each and every servo and extension. Switches and batteries, too. After you have ruled out each item one at a time, start over. Insert one item, then another until the problem re-occurs. Avoid any kind of Scotch or Mylar based tape on an antenna. Twice, possibly three times, I've solved a range issue by eliminating such a tape.

You eliminated the probability of the glitch being the JR servo when you unplugged it and a problem still remained. The engine was eliminated since the problem continues when it's not running,... unless you are running the ignition off of your receiver battery, or the ignition wire runs through the rx somehow. I certainly hope not. Just trying to cover all the possible bases.

DO NOT UNDER ANY CIRCUMSTANCES USE A PCM RECEIVER TO MASK AN INTERNAL RADIO PROBLEM. EVER!