sporsmaal

hello
i have a HIMOTO 1:18 SCALE TRUGGY with brushed motor
recently the esc (speed controller) has been acting strange.

switch it on, all is fine, seconds later it slowly moves backwards on its own, then quickly builds up to full speed.
sometimes randomly it will not move forward or backward
sometimes randomly it will only move slow, then let off the accelerator, apply it again and all is fine.

fresh batteries does not solve it. adjusting trim does not solve it.
im at a loss what to do
any idea whats going on and how i might fix it?

thanks