IHall

Hi all. I have just bought a 1990 VZ Legacy 5 speed wagon with normally aspirated EJ20 4 cam motor that's done 143,000 kms or 90,000 miles . Very happy with car, other than a mild-moderate engine miss or feeling of "surging" under load, most noticable between 2000 and 3500 RPM. (car idles fine and runs beautifully on light load such as cruising speeds). I have been told by the local Subaru dealership this can be caused by high mileage coil packs misfiring and have replaced all four ($$.. ..ouch), to no avail. Also have replaced spark plugs with both standard and then platinum plugs, as well as replaced fuel filter. Again, no improvement. Does anyone out there in Subaru-land have any thoughts on or experience with this kind of problem? Faulty sensor/s? faulty engine management computer? restrictive exhaust? (muffler has been replaced with cheaper aftermarket unit prior to me purchasing car) Am reluctant to keep throwing money at the symptoms without fixing the problem. I appreciate any thoughts or advice you may have. Thanks and best wishes, Iain