CEN MT2 monster truck

With radio on and truck on -the steering servo always works no matter what .

The throttle servo will work with the truck in my hand off the ground all the time. ( running)
Put the truck on the ground and walk away and it works.
start driving it and the throttle stops working (goes to an idle)( but the steering keeps working) If I walk over to truck and play with throttle it will start working again for a sec.
I have the truck on the work bench and there is nothing I can do to make the throttle stop working on the benck with the engine off.
Futaba 3PK radio with non digital futaba reciever.


I switched crystal in the radio to try another buggy and it works flawlessly.

What would be the most common problems to cause this?
reciever?
vibration causing the servo to stop?
the pull start rubbing on the throttle linckage?
I can swap recievers BTW from my other buggy as a test

BTW it is never a run-a-way. always goes to idle.
I'm starting to wonder if it is a setting in the radio.Hummm
I have 2 cars with 2 settings for each.


I started another thread on this topic here
http://www.rcuniverse.com/forum/m_11...tm.htm#1195580