My '02 Impreza 2.5RS has developed a problem. At highway speed it has a tendency to lose power, then recover. When starting from a stop, it "hiccups" several times before settling into a relatively smooth acceleration. At idle, it slows from 1100rpm to 600, then back to 1100, then to 500, then 1100, then 400, almost dies, back to 1200, and if I let it go long enough will eventually die. The hesitation and stalling during acceleration and at speed are worse if I let it do its idle dance long enough (as after being stopped at a light). I found that the hose connection to the air filter assembly was loose, although I've never touched that, and the air filter had a good amount of "oily" residue (just replaced it) and an unexplained hole, like a rock had gone through the filter. Originally I thought it was water in the fuel filter, as with my first '84 1600 sedan, but that is unverified at this point, as, without a manual, I can't locate the filter. Further, I've read on this site some post re: MAF contamination and the resulting mixture problems. Any thoughts or advice would be appreciated.
Stan