1998beetle running rough has code p1300

oxygen sensor bad, cataylac converter plugged

A broken valve, a bad spark plug wires, or spark plug wires loose.

you have a bad igniter ( spark plug coil) you can check by disconnecting each coil and see if theres any change in the rpms if you notice a change the coil is good if not the coil is bad what year is your car?

cylinder 1 getting too hot causing ceremic crack could have wrong heat range plug in which spark plug too hot.or need replace spark plug wires.one plug wire could be bad best replace all spark plug wires.

It's bad enough to have a steady engine light, but to flash...really not good. A flashing engine light means the vehicle is in "limp home mode". Enough to get you somewhere to have it fixed immediately.

All sorts of issues could be the cause here from plugged injectors, plugged fuel filter, bad spark plugs, bad coils. You need to find out what the codes are that are stored in the computer to provide more detailed clues as to what's going on.

A flashing CEL means that you might be causing damage to your CATs. It will flash when the PCM senses a misfire bad enough to cause fuel to dump into the exhaust. When that happens lay off the throttle. Chances are you've got a bad injector or bad plug.

Use a code reader to know the real reason that check engine light come on.

it`s a good idea to get a complete tune-up with 155k. but you can use a scanner to get a code to find the problem.

I’m happy to help further over the phone at https://www.6ya.com/expert/kenneth_3efc1f8510674f04

it might be an injecter that is bad. you need to ohm out each one and the onr that is much diffrent from others is the bad one.

Do you know if the plugs were changed, a bad or broken plug will also cause rough idle and slow acceleration?

The reason the check engine light is flashing instead of on steady is because it is missing bad and the car companies did this to tell you to stop the car as soon as possible to prevent damage. That is the only time the light will flash off and on instead of being on steady.
The cause is a little harder to diagnose. It could be a fouled spark plug, a bad plug wire, an injector, stopped up fuel filter. I can't remember if that car has the distributer or the coil packs but you could have a problem there. If you have never changed the spark plugs or fuel filter, it is well over a hundred thousand miles to do so now. They say to change them at one hundred thousand but 50 to 75 thousand is better and you will get better mileage. The fuel filter needs to be changed every 20 thousand miles now days because of all the cheap gas we have to put in the cars.
This is for mechanics or technicians. If no one out there believes me about the mileage on the fuel filter, then take the filter off and see what comes out the back. Looks like black water to me.