When you changed the plugs, did you install stock irridiums? When was the last time wires were changed? If it's been a while fire it up in the dark and mist some water over the plug wires and see if you get a light show. If you do, then the wires are leaking voltage. If you still have the stock metal plug wire heat shields on I would junk those too, they're not needed.

Would also be a good time to remove and clean the MAF with approved MAF cleaner (don't use brake/card cleaner).