I have over a few years noticed a gradual lack of pulling power/gutless.  Last mot mentioned engine seemed to be throttling back???. I have noticed that the vacuum actuator for the inlet manifold run butterfly control does not pull in when vacuum is present at start/normal revs <4,200 rpm.  Also vacuum was being lost less than -20 inHg say -17inHg. I tested the vacuum supply to the vacuum actuator alone with the actuator out of vacuum cicuit.   I read -21 inHg excellent, no losses so far. I t