Originally Posted by Sweet Mercy
for whatever reason was cured when a local engine builder guaranteed me that using Bosch copper plugs instead of the NGK IR would solve the problem and he was correct, the car was smooth! He said the car, with that kind of mileage, simply didn't burn as clean/good as it did when newer and that the car was running a little richer than it should.
Take the car to someone who knows Subarus. You have an underlying problem that needs attention. Properly gaped iridiums don't spark any differently than the coppers he put in. Now you need to change your plugs in 20-30k miles.