FYI I raised this issue on here a year ago. So if it's familiar to you, that's why. Long story short, water got in my fuel system two summers ago and messed up my '05 Subaru Impreza RS real bad. No computer codes went off though, so technicians were pretty much helpless. Right away, the dealer gave it a tune up, which did nothing. A friend told me the problem was probably my fuel filter. He was 90% right. I changed the filter and most power was restored.
It’s still cruising about 7-8 mph slower than it did before (at 2k rpm, an ’05 RS normally rides at about 57 or 58 mph, I can’t remember. Now it cruises at 51 mph at 2k rpm.) Plus, acceleration is moderate to poor, for a subaru. It just feels like a compact kia or something - loose, or weak, like it’s not getting enough gas somehow. It’s not as responsive as it was before this water fiasco… like a normal Subaru should be (real touchy off the pedal).
As no technician has been able to provide any help, and I am no mechanic, I’ve spent over a year and a half taking very expensive shots in the dark. Here are the parts I’ve thrown at it:
fuel filter/pump (same assembly)
mass air flow sensor
fuel pressure regulator
I also had the gas tank drained.
One tech found the transmission burned out. So that had to be replaced.
One tech cleaned the throttle body. That made a very minor difference in power.
So I’ve come to the conclusion that there’s something going on in the throttle, like it's not releasing enough gas. I saw how some people, including an impreza owner on a different site, tightened their throttle cables for whatever reasons and got some kind of result. That lead to me to believe the throttle could be the source of my problem. I had a mechanic look at it and he said that my throttle is electronic – no cable.
The problem seems to be between the pedal and fuel injection. Could there be a calibration issue going on in the throttle?