I tried swapping an automotive TPS, but the indexing tab was in a slightly different location than in the Merc. TPS. After reinstalling the original TPS, engine ran almost perfect. Chased blue fin tuna for much of Monday, trolled for hours, the engine went back to 600 rpm each time. I suspect the slight variation when bolting the TPS back in place helped, or possibly there was some unseen corrosion on the contacts.
A real Merc. TPS in on the way, most likely this will clear up the rest of the problems. In retrospect I should probably have changed some of the sensors months ago. Engine now has 2,000 hours on it, sensors go eventually.
Only issue remaining is that once again engine will not run between 600 and 1,000. Local dealer told me that is the way Merc sets up the engine and that there is nothing that can be done about it.
Alldodge, thanks for all your help and educating me on some of the nuances of this modern engine.
