(posting this for a computer illiterate friend)
The transmitter is a 6ex, each plane has it's own R617FS receiver and set of 3004 Futaba servos. On plane "1", the throttle servo started acting up, and wont idle down like it used to. The linkage is not binding and nothing has changed since plane was flown last. We pulled the plane's hatch and watched the servo arm "jiggle" back & forth as the throttle stick was advanced. With the transmitter throttle stick fully closed, the engine is revving at half throttle. Adjusting transmitter throttle trim up & down behaved as expected but not enough to fix the idle speed. We rotated the servo arm one gear and that got the idle speed more normal, However with the the throttle stick fully CLOSED, putting a tiny bit of BACK pressure on it (against the stop) makes the servo rev the engine HIGHER. Release the back pressure and servo arm closes the throttle slightly. Advance the stick and the servo arm jiggles back and forth as it travels to full open. All other channels work perfectly.

On plane "2", after flying normally all summer, the elevator servo developed a mind of its own, while all other channels still work perfectly. Touching the transmitter elevator stick makes the elevator servo jiggle wildly for a few seconds until it settles down and remains in position.

If the transmitter went bad, why does it affect the throttle on one plane and the elevator on another?
If the transmitter is ok, that means 2 different receivers or 2 different servos went bad at the same time?

Any ideas?
thanks,
Bruce