Like I said I have had the same problem twice.

Once it was the ignition module itself. replaced the module problem solved. again the servo thought to be bad tested good.

Second time it was the power wiring touching the throttle linkage ( all plastic nyrod) changing the wiring a couple of inches fixed the problem.

If you had a switch on your ignition power wire it would be a very simple test to try the servo with the ignition off.

Mly vote is servos are still good and you are getting RF noise.