Hi and welcome to the forum
I've had the same problem on my PT...just like you, i changed the plug and wires 3 times, air filter, check for bad connections in the electrical area and like you, the car was running good for a couple of days and then it started again, i have a 04 cruiser na with 95000 kms and i had it for a year now and it still the same, i tried asking questions on this forum and never got a reply that could fix the problem. Realy hope you'll get good help, and i'll keep watching your post to see if you get lucky and this way... i'll get lucky to
Good luck to you.