Sounds temperature-related and might have something to do with the temp sensors
also. I'd check both of them and watch the temp gauge. If you drive fast for
a while and suddenly slow down your temp goes up because the cooling system's
efficiency is related to water pump speed but the engine heat lags behind
so when you slow down the engine is still hot from running fast and it takes
the cooling system a while to catch up. Meanwhile if the D-jet thinks it is
very hot it will make the mixture lean, possibly too lean to start.
On the other hand if you have a sensor problem it might think that the engine
is cold and may run it so rich that it floods instead of starting.
I guess you have double checked ALL the FI ground connections....
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George Downs, Bartlesville, Heart of the USA!