Toyota Repair: Avalon spark plugs, spark plug wires, scantool

Question
Ted, a spark plug in my wife's '99 Avalon went bad. It fell apart in my hand. I replaced all 6 spark plugs and the car ran fine for 1 week. I then replaced the spark plug wires and now it barely runs at all. No power, very rough. I thought that maybe the wires were not put on the right plugs, but switching them just made things worse. What can I try next?

Answer
First of all make sure that the spark plug wires form the coils on the front of the engine(the left bank) are correctly installed to the spark plugs on the rear(right bank)the wires should have numbers on them, the rear bank is numbered 1,3,5 and the front bank is 2,4,6, one coil fires two spark plugs. There have also been problems with the coil packs failing and causing a misfire and loss of power.
It may be a good idea to have a toyota dealer hook up the diagnostic scantool to retreive the misfire code, this will tell me which cylinder is causing the problem.