this could also be a fuel problem, like injectors clogged with gunk or whatever, i had this problem, my filler tube was rotted onm the top and i didnt know it, so it kept putting crap in the tank and it was enough to get passed 2- filters i had in the system. i kept cleaning the injectors, and they kept clogging back up faster and faster, anyways, the morrell of the story,

take the injectors out, clean them with carb cleaner or TB cleaner, blow them out with air, ect, see if that works, its about an hours job for me since ive done it a dozen times or more