2002 Prius, P0420, 37.4MPG, Misfires, High RPM

have you tried switching injectors to see if the misfire moves?

 

The next thing I would do is swap the #1 & 2 coils with the 3 & 4 and see if the misfire moves. While you're doing that carefully inspect the wiring and electrical contacts and the like.

I'd also tell you to check the compression, but on this car I have no idea how one would do it since there is no starter to control. Perhaps others here know something of checking compression.

 

I would not get into injectors just yet. It's much more of a PITA than swapping coils and - probably - checking compression. Start with the simplest and move to the more complicated.

By far the simplest first thing is to just swap the 1/2 with the 3/4 coils and see if the misfire moves to 3/4 (P0303 & P0304) rather than 1/2 (P0301 & P0302). Cross your fingers as that would be an easy answer, but if nothing changes - you've eliminated the next simplest thing and know to move on. So the next move would be compression.

Yes, to check compression you pull a plug, thread in the gauge and crank. The only reason I'm not certain about the nitty gritty of how is that you don't control the starter the computer does. On a "normal" car you control the starter with the key (so long as the electricals are in order). Your turn of the key sends the juice to turn the starter and you decide when to turn off the juice to stop the starter.

I've not had an ICE no start or a need to check compression on my Prius, so I'm just not sure how it works with these. With the computer "deciding" to operate the starter, if you disable fuel delivery and spark (which you should do for a compression check), and turn the key I have no idea what the computer does w/ the starter. If it will just crank it for a while, great. Then do it. Someone who knows will hopefully show up to clarify.

 

Unfortunately, I can't answer the Q about checking compression or what it means on an Atkinson cycle engine. It's quite possible that you will need a Techstream to command cranking to test it. And while I''m pretty sure that the compression should be just "normal" (say 150-200 psi) I'm not even sure about that. Hopefully someone else on the boards has an answer.

I would just mention that the misfire is probably more than once in a blue moon since you say that the car shakes upon start up. But having it be frequently or long lasting enough for the computer to set the code might be the once in a while part. It's not as simple as "computer sees a misfire, so computer sets code" just because if the computer threw out codes every time an anomaly came through the wires today's cars would forever be lit up like Christmas trees. So normally a code is set after X anomaly has been recorded X number of times within X time, or X number of times in X numbers of consecutive drive cycles and the like. If you do get a powerful enough scantool you should be able to access a misfire count for each cylinder. It will be expressed as a percentage and it has to get high enough for the computer to toss out the code. At least, this is how it typically works.

 

Perhaps not on the high probability list, but... gasoline quality?
Try a tank of ethanol-free premium and see if the problem persists.

 

(Well, the point of swapping coils was to check it out w/out spending $$, but new ignition components can never hurt...)

I am not a transmission specialist - and there are transmission specialists. Most mechanics, including those at dealerships, don't know squat about transmissions and even fewer will know the Prius CVTs. That said, every transmission specialist I've ever talked to says NO! to a "transmission flush." Drive it another 2-5K or so and drop the pan again.

I've never dropped a CVT pan (though I'm also belated in getting to mine on my '03), and don't "understand" then as well as typical automatics. But in a typical automatic, the magnet fuzz is just normal. The particles are not normal. Were they metal particles?

Whatever issues in the CVT this is going to be unrelated to any rough start-ups. You mentioned cleaning the throttle body, but have you cleaned the MAF sensor? (That's an easy one). And if you hook up your scanner - when you first start the car does the engine coolant temp approximately match the ambient air temps (or whatever the under-hood ambient temps would be if you're, say, sitting in the sun. Watch the coolant temp and see what it does when you start, as the car warms up and then up at full operating temps. Same with the actual air temp sensor - actually with the car cold and not running, those two should be in pretty strong agreement about what the temps are.

What is the status of the check engine light/misfire codes? And of the problems under load like on hills?