if i install a computer chip in my fj for better gas mileage and horsepower will it work and will it harm the engine?

My only suggestion is before you do that make sure it will not void your warranty. OK not only. I know at least 3 guys that bought those chips and it changed nothing. The Toyota engineers are superior to aftermarket outfits and in my humble opinion and rationale if the chip was better Toyota would use it factory.

would it be better if i got one straight from toyota then and had them install it? obviously i dont want to waste my money if its not gonna work.on the flip side i will spend the money if it does

most factory warranties would be voided if you add a chip because you can cause premature wear and failure (not that it would for sure happen, but it could)- the factory is not responsible at that point- you are. typically the changes the chips make shorten the life of components.

Those chips are aftermarket only. Toyota does not have /will not install them.

and Ditto on Richard. Excellent answer that I agree with.