I haven't gotten to the bottom of that issue yet. I asked him to try a number of things and let me know what he found. I can give you the list as well.

1. Remove the IC and re-install it in the socket (one guy reported this issue and I sent him another unit. Removing the IC from the socket and reinstalling it seem to fix the problem forever.
2. Move switch to position 7. hold down BOTH buttons and turn the power on. This does a complete factory reset setting everything back to as it came new from the factory.

I expect you have a problem with a sensor but trying the above two things will rule out other things quickly.

In order for the engines to pull back one of the RPM sensors has to be losing signal. Now we have to figure out which one it is. One thing that may work (I am on vacation this weekend and can't try it) is to connect engine1 RPM sensor to a Y cable and then plug it into RPM1 and RPM2 sensors. Run engine1 watching both engine1 and engine2 servos to see if they ever pull back. Now repeat the process with RPM sensor#2 connected to both Engine 1 sensor and Engine2 sensor via a "Y" cable. Run engine2 and see if either servo ever pulls back. This might confirm that both sensors are working properly.

Do the engines stay in sync the whole time that they pull back? What happens after they pull back - do you have throttle control or do you have to go to idle (below sync point) to regain control?