Any ideas?
 

Hey, I can't figure out what's going on...here's the story. I'm driving normally and stopped at a light. The car just stops and won't restart (battery is cranking, but it's not turning over). Have it towed to Mazda and they say it needs new plugs/coils/wires. I had just replaced them 4 months prior (less than 1,000 on them). So instead of paying the dealer $900 to replace them, I put on my old used set (about 20K miles) just to get it running again. It started and was driving fine, but I had a CEL.

I drive for about 5 days and then while driving, it makes a strange noise and starts riding extremely rough. It only goes about 1/2 mile then dies again. Same problem (cranks, but no start). I figured it's because of the old plugs. I buy a new set of plugs/wires/coils and install them yesterday. Car starts and runs but I still have a CEL. I just don't want it to die again...any ideas of what the problem can be?

1st off...............never drive with a CEL on for repeated lengths of time.
2nd............go to an Autozone or Pep boys or somewhere and get the code read and then come back and tell us what the code is. We can guess all we want, but if you're not willing to go get it read, then we can't really help.
3rd..........I'm going to guess that your CAT is dying and the code will be an O2 sensor code, but it could be something else.
4th....go ahead and give us all your info on car.............year, manual/auto, any history, etc.

Took it to autozone and this is what the guy said:

1) cylinder 1 is misfiring
2) need to check/replace Crankshaft sensor
3) need to check/replace back O2 sensor

Car info:
2005 M/T with 52,000 miles. Only mods are suspension and a K&N drop-in filter

So, you think it's the CAT thats causing the problems?

Misfire is usually plugs or coils. There are vendor here that will give you a good price on those(Mazmart etc.).
Crankshaft sensor = ESS, there are some DIY's on cleaning that and resetting it if you are even remotely mechanically inclined.
O2 sensor.............well, Mazmart(a vendor here) has them on sale right now. Do a search on "O2 sensor".
To me, this one is the scray one because it might mean that CAT is going. Next time you drive it, when you get done......look under the car and see if anything is glowing red. If so.............well, it's the CAT. Good news is it is covered up to 80k miles!