I think rule of thumb is a useful and quick way to make a generally good choice, and I have plenty of them. But what do you mean by rule of thumb ethics?Does anyone have some thought about infps and rule of thumb-ethics, versus utilitarian ethics?
I would not say infps are all utilitarianists, but I have got the impression (could be coloured by my own approach, that I notice similar ones more perhaps) many tend towards that side of the spectrum more, not having a very rigid sort of ethics.
More than being strong I see it as though ethics is used more broadly, that it is present in most considerations, and that it has the last word so often, over say efficiency or desire or duty.
In ethics, virtue answers the question “What is the right sort of person to be?”, in contrast to duty, which answers the question “What is the right thing to do?”.
However, there is another understanding of morality which should not be forgotten. This is the sense of morality in which morality is linked with certain virtues, excellences, or flourishing ways of living. In this sense, morality is not primarily concerned with rules and principles, but with the cultivation of certain dispositions or traits of character. This view has been expressed in this way: ‘The moral law ... has to be expressed in the form, “be this”, not in the form, “do this” ... the true moral law says “hate not”, instead of “kill not”...... the only mode of stating the moral law must be a rule of character.’ 
In contrast to the more restricted notion of moral excellence as the fulfilment of moral duty, the Greeks wanted to know what kind of life is best suited for a human being. What kinds and range of activities are required for a person to lead a flourishing life? To lead such a life would be to lead the moral life par excellence.
Thanks for the link, that was an interesting readI would say the nature of Fi is one of appraising things for their value and importance.
How it translates to real life could vary, I think it means that we have a reaction to certain things that sort of cross lines to what ever internal sense of good and bad we have.
This may or may not follow into a congruent behaviour of that value depending on the circumstance.
Looking at Fi there is this post I thought was rather sweet, to what extent it's true may vary though.