I had heard about engine wiring harnesses failing due to faulty insulation so I decided to inspect my harness. The classic symptoms are intermittent check engine lights end EA faults causing the drive by wire throttle system to go into limp home mode. My car was not exhibiting any of these symptoms but inspection of the harness showed lots of failed insulation and several 3-4 inch lengths of BARE WIRE. Given the condition of the harness I was amazed the car ran at all.
The replacement of the harness did solve one problem I had been having - at idle the engine would sometimes stumble a bit. Almost like it was losing a cylinder for a split second. With the new harness installed the idle is a smooth as glass.