Try cleaning or changing plugs. Klaus showed me great technique for shutting down. This has made hot starts and fowling non issues. Lean for 20 seconds at idle the. Turn off ignition at the same time you ICO fuel. When you go to restart don't touch mixture until engine fires. Works great every time.
On a 1.4 hour flight in leaned cruise the drop off on both A and B was 60 rpms each.
At 4500 feet these were my numbers:
21.2 MAP
2300 rpm
oil pressure 74
oil temp 178
CHT 343/338/333/338
EGT 1333/1388/1326/1388
fuel pressure 26
5.6 gph at 64% power
O320 160 hp Lycoming Fi dual lightspeed 11
I still have a drop of of 60-70 rpms leaned 1700 runup on A and B.
Any thoughts? The plane fly's nice and smooth in cruise. The stumbling on final and taxi is concerning and can be helped somewhat by leaning.