Intake Leak
The EGT was rising when I reduced power from 23" down to 16" when approaching an airfield. It would go from about 1370 with a full rich mixture all the way up to 1550. Pretty startling when I noticed it. Enrichening the idle mixture mitigated the issue but it still rose to about 1420. No idle cut off lean rise in rpm on the ground either. Did a careful inspection and noticed that the intake coupler for cylinder number 4 was almost all the way off the intake manifold. Almost an inch of tube was showing next to the crank case. Removed and installed a new coupler. Cleaned and painted the intake riser tube. Cleaned off the intake manifold face. It was a few hours of work. Now, without adjusting the idle speed, it idles at 520 rpm instead of 650. Just a few more adjustments to do and I think it is all tidied up.
