FYI, any opening in the engine vac system will cause things like you have talked about in you post above. Even the small "O" ring on the oil dip stick can cause misfire problems. These engines require everything to be sealed. You let a leak develop in the vac system and "bang"--you've got problems.

IMHO
Cheers.

 

+1 on that

 

Chuck, thanks for confirming my suspicions. As soon as the problem went away after I put the oil filler cap back on, I suspected that the problem was more that the "closed system" was compromised, resulting in the deterioration in engine performance. Has been running great ever since.!!!