87 Coupe GT starting, MPG malfunction

[Brian Raymond <padrino@umit.maine.edu>]

I was wondering what causes the average miles to gallon and mailes to
empty to mess up.. I just got my car a week ago and they worked fine. I
put in some fuel injector cleaner and about a day later the mailes per
gallon started reading 255 and the miles to empty 1515 (max value I
assume). My car also won't start now when its cold out, it takes like 5
min to start and once it does it won't accelerate at all for a couple of
minutes.. Does anyone know what happened???