2001, Engine Vibration (missing badly), Flashing CEL

My 2001, with 380k miles (1/3 Million!!! | PriusChat), started missing so badly that it is shaking, and the CEL is flashing. I pulled the codes, and got: P0300, P0301, P0303, P0304. It is obviously misfiring badly, and I know I shouldn't drive it until the issue is resolved to prevent damage to the cat converter, etc.

The google has suggested the problem is most likely ignition related, either plugs or coil paks. I don't even remember when I last replaced the plugs, and I'm almost certain that the coil paks are original to the car (or are at least 280k miles old, as I bought the car with about 100k miles, and I have never changed them). So my instinct is just to replace all the plugs and coil paks. But the multiple codes suggest it is misfiring on multiple cylinders. Does this mean its not likely plugs or coil paks, since it is unlikely that multiple coils/plugs failed at the same time? Does that implicate the fuel system? Anything else I should check?

There are pretty cheap coil paks available online (Amazon, etc.). Anybody have any experience with them?

Thanks,

 

I started it up after work and it ran perfectly. So it's intermittent.

I don't think there is oil in the coolant (no foaming on the dipstick, no coolant smell, no steam in the exhaust)

Since I got misfire codes on multiple cylinders, I like the idea of trying the MAF, since it's relatively cheap. I cleaned the throttle body already, and that made no difference.

Thanks,

 

It ran perfectly again this morning, and at lunch. Yesterday morning, shortly before it started missing badly, I went to one of those "dollar car washes." Is it possible that I somehow got water somewhere I shouldn't have? I have heard of leaking cowl seals allowing water to get into the spark plug wells, etc. I didn't see anything like that, but I don't think I actually looked closely until later in the day when I had a chance to pull a COP, so maybe it had dried by then.

Thanks,

 

Started running crappy again just before getting back to the station Friday afternoon, after running well for two (9 mile) round trips to the office. I looked back at my records, and I replaced the spark plugs not that long ago, so I will wait on those. I have ordered a Denso MAF sensor from Rock Auto. We'll see if that takes care of it. Thanks.

 

When I pulled the codes the first time this happened, I got misfire codes on multiple cylinders, which is why I am looking at something that is not cylinder-specific.

 

Well, a new Denso MAF didn't fix the issue. After replacement, it started running very rough on the way in to work. Now getting only a 304 code. I'll try swapping the #4 COP onto another cylinder first, and see if that "moves the miss." If not, I'll try swapping the #4 injector.

Any other ideas?

 

The 304 code means its the 4th cylinder in the firing order, which is the #2 cylinder (1-3-4-2), right? And the #2 is the 2nd from the passenger side, correct?

Thanks,

 

Thanks,

Can you, or anyone else, confirm that the 304 code means the #2 cylinder (4th cylinder in the firing order, 1-3-4-2)?

 

Thank you ronlewis. I appreciate the quick replies.

Google searches also find some cases where this issue was caused by clogging of EGR passages in the intake manifold, or clogging of the EGR cooler. Is this applicable to the Gen 1? I realize that the COPs, plugs, and fuel injectors should be verified good before heading down that rabbit hole, but I'm just curious whether the EGR clogging has ever been documented in the Gen 1's. My car has lots of miles, so egr clogging definitely seems like it could be possible/likely.