Well, I'm now into about 1 month of owning the 02 GT. Last week I thought the loss of power was imaginary. After another tank of 87 octane a distict rattle could be heard as I accelerated going up hills in 5th and 4th. The engine did not like to apply any torque under 1500 rpm.
I know the previous owner swapped gears at some point. The speedometer is correct, so that tells me a tuner was used. It appears the car was tuned to 97 octane also. I put a few gallons of VP 103 octane in (it's what I had at the moment) and drive to the gas station and begrudgingly filled up with 97.
Suddenly the torque and power are back, and it appears the spark knock has gone. I am glad I don't have to change plugs at the moment. I'm a bit worried about blowing plugs out of the head on this fragile 4.6 engine. I'm not exactly happy about fuel that cost twice as much, especially with the Summer has prices.
I have a can of electrical cleaner. The car has a K&N filter. I may as well clean off the MAF while addressing the issue as completely as I can.