I bought a 99 Legacy with 80000 miles not long ago. Not knowing what the previous owner had done, I started replacing everything just so I knew things were in good shape. That worked great until I put new spark plugs in. I put in Bosch pure-platinum four-prong plugs, and he car ran well but it had no power going up hills. I talked to a couple of Subaru mechanics, who all suggested putting the plain NGK plugs back. So I bought four new NGK's, checked the gap, and put those in. The car would start, but idles really rough and can't even make it up my driveway with the gas floored. No engine indicator lights come on at all. So I put the Bosch plugs back in...same performance as the NGK's. The car is now completely undriveable. I'm going to swap out the plug wires today and hope that fixes it....any other thoughts?

In another example of why I hate to work on cars, the problem turned out to be a bad mass air-flow sensor. According to the mechanic who figured it out (after about two hours) there was nothing that could have caused that as a result of changing the plugs, it was just an unhappy coincidence. The question now is, do I have the guts to go ahead and install the new fuel filter I bought when I bought the new plugs?