This situation was about 30 years ago, but it taught me a lot about not taking anything for granted when doing engine diagnosis. Plugged/restricted exhaust systems can cause a lot of oddball symptoms that are awfully hard to find!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!