I have a 2002 Outback sport. I began having hesitation problems about one year ago. The hesitation would only occur after a fuel fill up and last for about 1-2 minutes then gone. Did not occur at idle, only when driving. Now, I've been having the issue at varying fuel levels regardless of fuel fill up or not and the hesitation appears to be worsening. The Knock sensor has just been replaced with no improvement in the hesitation.
I've suspected the fuel filter, water in the fuel, what else? Any thoughts?