My CP2 has started to live its own life. When waiting with throttle at 0 it behaves like someone is pushing the throttle up and down again very quickly. This is prevented by giving just a little throttle so the rotor rotates slowly. When flying, sometimes it "gives itself" a little extra throttle and climbs up, so far, I have managed to get the control back again. I have tried to change crystals, and get the same result. All conditions (local, temperature, antenna and so on...) before and after this problem appeared are the same.

My friend has almost the same problem with his new King2. Sometimes it throttle up by itself, sometimes the rotor stops even if throttle is on and sometimes the rotor is rotating even when throttle is at 0. Tried different crystals here to. We also tried my (I have a new King2 as well) radio without result...

well it sounds like it's either interference or the esc is acting up.

Oh I did'nt think of the esc. Yes, that might be the problem with the HBK2. But how about the CP2, do I need to replace the 4 in 1 unit?

Actually, it sounds like a dirty potentiometer (pot) on your throttle stick. If moving the stick slightly clears it up temporarily, then the pot would be my guess. To fix it, you would have to open the transmitter and spray electrical contact cleaner so it goes inside the pot, while moving the throttle stick.