Scott,
Sorry to hear the problem is still present. I was wondering if there is any way for you to read the engine management data live with a scanner. I have done some work w/ ECU's in the past on both race and street cars and have often found problems by viewing data live or recorded. I know that on Hondas I have worked on we have been able to watch channels live to chase intermittent problems.

On the race stuff we just used our logging equipment to chase engine problems with some creative wiring. I am no software guru, but am familar with some of the racing datalogging equipment (Pi,Motec) and depending on how desperate you are you could hook up a system to your street car to isolate the cause of the problem. I is possible to pick up "obsolete" Pi systems for reasonable $ and they will log whatever you may like! The only limits are logging frequency which is $ dependent.

Well, I know this offers little in the way of a solution, but it could help in diagnosis.

Andy