Sometimes the intake pipes on Lycoming engines can come loose. This will cause an intake leak, usually indicated by a rough idle and higher EGT on the affected cylinder. The leak will also leave a tell-tale sign of dark material around the pipe from fretting. It takes a special internal swaging tool to reseat the pipe.
In Case You Missed It
Guest Editorial
We've made improvements: This year's printed Kit Aircraft Buyer's Guide has a new format that highlights the latest designs. Plus, the Online Aircraft Buyer's Guide's new features yield a better and more useful search result.
I had loose intake pipes starting around 1000 hrs. Tried some proseal around there which worked as a stopgap but eventually I found an engine shop that was willing to loan me the swaging tool. Lucky! Now all tight and good.