2008 2Gen w 190k - Misfire 300, 301, 303

"Misfire" on 1 and 3. I heave learned more about our Prius in the past month thanks to this forum and videos than I have since in 14 years of owning it. Mainly it is because it was the wife car and she didn't want me to touch it, ha ha, but now it is mine. We have oil consumption of course and probably ran a little low here and there, but it has been maintained fairly well and mostly at the dealer.

The problem: We get the occasional engine shake in Park, it will go away when put in neutral or if I toe-touch the accelerator slightly to raise the RPMs.

Done so far: Correct Denso Plugs changed with new coils 10k miles ago, just checked and cleaned plugs again (little oily threads on 2+3), ran a tank of Techron through and on my second tank, I have some fuel injectors ordered and on the way as I think I still have the originals

So I have read many threads and possibilities, from head gaskets, to rod bearings, to injectors, to VVT solenoid, to PCV valve, to MAP/intake cleaning, to fuel pump, but it drives great other than the occasional shake session which goes away. It could be a small amount of water in the cyls, and runs better as that gets evacuated, but it really seems like if it was such a small amount it would run better more quickly, but shaking seems to persist unless I put in neutral or touch gas. It seems more like an ECU mode it gets stuck in, like too rich, or poor fuel flow at low RPMs, or some low idle/advance condition.

Of course I feel like it is running better, but the CEL/MIL light comes on with those codes after they are cleared. After I cleaned the plugs it seemed better, I only got one code 303, but eventually got all 3 codes again.

 

Sorry I realized I didn't pose a question.

Am I in denial, should I just immediately pay for a leak-down test to confirm health head gasket?
Do the chemical coolant tests work if I have a very small leak in cyl 1 and 3?

My old coolant looked pretty good, didn't see much of an oil sheen on top of the coolant in the bucket, maybe a small spot. One thread might say assume it is a head gasket, another says to assume it is a rid bearing, and another said they fixed their rattle with 6 tanks of Techron, ha ha. I guess I was hoping to find 3 videos showing the different noises and rattles for each of the causes.

 

UPDATE: I replaced all 4 injectors with eBay refurbs and I think that fixed the rough idle, shake, rattle, and knock. I knew it wasn't related to MAF, PCV, or throttle body dirt since it was cylinder specific misfiring on 1 and 3 consistently. I could have swapped injector positions to see if the misfire moved to the other cylinder, but when refurbs are about $10 each on eBay I think it makes sense to replace them all. It wasn't that hard, but definitely not for the average owner. I am still not sure i don't have a fuel leak at the injector rail, nothing visually leaking, but the smell of gas lingers so I am waiting until morning to see if it still smells.

MIne sounded just like this video, and if yours makes this noise then service or replace the injectors:

If you have a Gen2 and about 200k miles on it and you get the shake, rattle when in Park, but it goes away in Neutral or in Gear or with a little more RPM it is stuck injector. All of my old injectors had the same 14.3 resistance, so there was no obvious failure, but clearly something caused the injectors on cylinders 1 and 3 to stick or spray unevenly at idle. I used Hobbits depressurization method of depinning the fuel pump at the driver kick panel connector.

I will report back if I did end up having a fuel leak on the rail, or if the shake.rattle returns or I get any other new problem.

 

Thank you, I had read a lot of your posts before doing it. We had already replaced plugs and coils with improvement, so I don't fault the mechanic my wife went to for trying those easier things first. This video just helped convince me to try injector replacement since the in-tank cleaners didn't help at all. If the misfire is intermittent and primarily at idle I'd lean more to injectors than toward plugs/coils. I am going to take another look at it this weekend to be sure I don't have a leak. I am not 100% sure I am smelling fuel, I might need to smell another Prius to be sure, ha ha. I should see fuel or really, really smell it if it was leaking on the pressurized side from the fuel rail o-ring, I don't see or smell that, but I'll just pull it apart again to be 100% sure.