I would reccomend checking both wastegate (actuator) and compressor (turbo) hoses to the amal valve, also check for corrosion in the plug at the amal valve of a broken wire. Also, as mentioned, check the actuator for leakage ie the capscrews if they exist. Also, the diaphram inside the actuator might be on its way out.

The worst case scenario is that the penny inside the wastegate might be broken.