Problem with autopilot and altitude/cyclic hold

[Mr. Farknocker]

I'm having difficulty in holding altitude when the altitude/cyclic hold is activated. A short while after being engaged, the Mi-8 will decrease and or increase in altitude in a cyclical manner.  If I'm near the ground when the AP is engaged, it often leads to catastrophic results if I'm not paying close enough attention to grab ahold of the controls to regain altitude. This happens when all three AP buttons are activated. Am I doing something wrong or is that how it works and constant monitoring is always required?

[engines]

I find that system-induced pitch oscillations can occur when the altitude is engaged if one or both of the following are true:

 

- the aircraft is not already perfectly trimmed.

- airspeed is greater than 200kph.