I'm going to apologize in advance for a lengthy post. I bought my '02 WRX Wagon back in March and I've been dealing with the same persistent vibration the whole time I've had it. I've literally spent hours researching this forum as well as many others and still haven't figured out my issue. So, I thought I would finally make a post and see if some of you can drop some new ideas on me. Here's the run-down on the car:
'02 WRX Wagon
Mods include Cobb catted downpipe, Cobb Stage 2 AP Tune, and Flowmaster Axle-back exhaust, everything else is stock. All mods with the exception of the Flowmaster exhaust were added prior to my ownership.
The vibration I get is really felt between 70-75 MPH in 5th gear, which is around 3,000 RPM. However, I can rev the car in neutral sitting still and feel the vibration in the gas pedal, so I don't believe it's actually related to the speed I'm going. That should rule out bad axles, unbalanced tires, etc... I think the main reason I don't feel it in the lower gears is because I pass through that 3,000 RPM threshold relatively quickly. The vibration is noticeable in 3rd and 4th gear, but not nearly as much as 5th gear cruising on the interstate.
In 5th gear on the freeway between 70-75 MPH, I get a slight vibration in the steering wheel and a pretty noticeable vibration in the gas pedal. The shifter has a good amount of vibration as well. But, this seems to be fairly common for these cars, if I understand correctly. As far as the gas pedal goes, I've checked to make sure the throttle cable is secure. But, even if the throttle cable was loose somewhere, it wouldn't explain the steering wheel vibration, unless the two vibrations aren't related. They seem to feel like they're on the same frequency, though, if that makes any sense. As long as I'm not in that 70-75 MPH (~3,000 RPM) range in 5th gear, I don't feel the vibration.
Have any of you guys experienced anything like this? Any ideas you guys might have on what's causing this would be greatly appreciated.
Here's a list of some things I have checked that seemed fine to me (let me know if I should re-check them):
1. Motor Mounts - used pry bar to see if they move at all
2. Transmission mount - ditto on the pry bar
3. Carrier Bearing - didn't seem to have too much play
4. U-joins - visually inspected for cracks, didn't see any
5. Tires - Brand new, also rotated fronts to back, backs to front, to rule out balance issues, just incase
6. Downpipe - made sure it's not vibrating against anything
On a good note, the car runs really great. I'm knocking down 24-25 MPG in my daily driving. Also, I've done a few full-throttle runs up to 80-90 MPH at an old runway and the car pulls hard through the first three gears and reaches around 14 PSI of boost. So, I have no complaints from a performance aspect.
The guy who had the car before kept records of everything that had been done to the car. All maintenance was done at a local Subaru dealership. The recommended 90,000 mile maintenance was done at 79,000 miles before I purchased the car.