This only recently started happening. The car is at about 160k miles and has a tremor to it, a bit more noticeable at idle. The CEL is solid when driving, but starts to flash if I have been driving for a bit and then stop at a stop-light. It doesn't flash when idling at start, just after it heats up a bit. I took it to a shop and had the codes pulled. One was a Cylinder 3 misfire, the other was a Random Misfire. I replaced plugs, wires, distributor cap and rotor... a bit better, but still had the light come back on.

I'm trying to do as much of this myself as I possibly can, as I have only recently started to learn how to do my own car work and want to use this as a learning experience. At the same time, I know a flashing light is a bad sign and don't want to end up damaging the car. I've been advised to check the ignition coil and check for vacuum leaks, but I thought I'd ask around a bit more first.

On a side note, I noticed something really weird today. When I hit the rear defrost (I think that is what it is. Little square with squiggle lines?) then the shaking gets worse. If I turn it off, it gets better.

 

Being an '01 with "wires" I can assume this is a four cyl.

Does this only happen once the car is at normal op temp, or does this happen when the engine is cold as well.

It wouldn't hurt to do a compression test of the cyl's to be sure there isn't something major going on. Many parts stores loan the tool out.....you put down some money....use the tool and then get your money back when you return it.

So check the compression and let us know the readings.

 

Beg/Borrow/Steal an OBDII code reader and pull the codes.
Post the codes. Those will give us better data rather than your description.

 

The codes were p0303 and p1399.

I will find someone near me with the compression tools and let you folks know what I find.