124 NO engine power at all speeds...

[J.HIDALGO]

worse on lower speeds.
Background: My car was running perfectly until yesterday. I went to a store and while waiting outside with the engine on (for about 10 minutes) the engine started to miss and shake. I turned it off immediately. I restarted the car about 10 minutes later and now I have a rough idle and lack of power throughout the power curve. The car shakes and hesitates when under load. It gets better and the speed increases. It is NOT temperature dependant because it happens all the time now. There are no lights on.
I bought a fuel injector cleaner and it is in the tank now (no change so far) but, I don't think it is fuel related.
After reading the archives, my two top suspects are ignition coil (because the problem is worse under load) and/or a plugged cat converter (since temperature can affect the cat and can cause problems under load). Is there a simple and accurate way to test these items. Although, I must admit that I do need a distributor cap and rotor, based on mileage alone.
My car has over 200K and is "eating" oil.
Any other ideas?
Thanks!