lifter
My money is on a collapsed lifter. Cue post #21 (Andy Cobb). I had a similar problem with a Superior-built engine, though the intake lifter on my offending cylinder never completely collapsed. I datalogged several flights, then reviewed the data on savvyanalysis.com and eventually deduced what was going on. Replacing the intake lifter guts solved the problem. Given how easy it is to swap lifter plunger parts on the average Lycoming I'd start there.
My money is on a collapsed lifter. Cue post #21 (Andy Cobb). I had a similar problem with a Superior-built engine, though the intake lifter on my offending cylinder never completely collapsed. I datalogged several flights, then reviewed the data on savvyanalysis.com and eventually deduced what was going on. Replacing the intake lifter guts solved the problem. Given how easy it is to swap lifter plunger parts on the average Lycoming I'd start there.