help-2004 Gen 2 sudden misfire engine shaking/shuddering low power.

Hello - thanks in advance for any ideas.

2004 Prius 215k miles.
Driving along on local roads and all of the sudden when I gently accelerate from coasting the gas engine shakes and shudders, low power, very unresponsive. Happily I was close to home and limped it home. No red triangle or CEL. Felt like when I got a "wet cylinder" years ago with water on top of Cylinder 1.
(when windshield drainage cowl path got clogged with unseen leaf debris at drain hole through metal firewall behind plastic drain assembly- and had misfire/fouled plug in 1 - and got it fixed by clearing drain, drying out spark plug well and putting in new ngk iridium plugs at 125k mi approx?

• car consumed oil in it's middle age - then when i switched to mobil 1 high mileage the oil consumption stopped.
• have been having gas gauge showing empty - when it's not empty - on and off. Reset after disonnect of 12V battery during hybrid repair/module swap out.
  
• recently swapped out two hybrid battery modules with good tested/reconditioned used ones from a local Prius battery shop to solve hybrid battery failure (after doing this same thing in Sept. 2020 also - removing bad modules that reared their head during spring 2020/covid when car sat a lot)- and it's been running great- lot's of ICE shutoff and battery only "EV" type driving at gentle/low neighborhood speeds, etc. Dr. Prius shows good hybrid cell function. Getting over 50 mpg for 100 mile trips when i keep it near 65 mph/less, 45-50 mpg when at 70mph.
• 12V battery is fine with 12.5 volts standing with car off.

Ok - so first figured I had bad spark plug or coil. Area on top of valve cover/at coil location looks dirty/oily. In addition there is oily small 'pool' when I look down through throttle body baffle down into intake area of engine after pulling air filter box. Pulled plug in cylinder 1 and sure enough it seems fouled with signs of oil - not water - in cylinder spark plug well. Pulled Spark plug from Cyl. 1 and it looked bad - line of brown/corrosion on plug - so I replaced it. Other three coils/spark plug wells seemed clean.

Started it up with new plug in cyl. 1 and same shudder/shake, no improvement. Swapped coil 4 with coil 1 - same thing. tried to test with coil connector pulled in each cylinder in turn one at a time to see if it did same with a cylinder fully off line to maybe give me a clue - and got red triangle and lot's of lights. codes from dr. prius showed P0300 P0301 P0303 P0351 - but only when I pulled connector from cylinder 1 coil - and then each other coil one at a time in turn - seemed the same regardless of which one was pulled - but when i did pull a coil harness plug - I'd get the dash lights and warnings, the ending would shut off and gas engine wouldn't come back on. Only if I powered down, reconnected all 4 coils/plugs and started would I get engine to come back on - with full shaking shuddering.

What is best way to eliminate other spark plugs and other coils - or any/all coils as the problem?

• Could this be PCV valve failure (with oil seen down inside through throttle body plate when it's opened - though I am not using/losing oil like I used to 8-10 years ago before switching to mobil 1 high mileage)?
  
• Or - is it the effects of oily cylinder 1 well above the spark plug and fouled plug (though new plug in cyl 1 and coil swapped in from cyl 4 didn't fix it)- though I don't think I overfilled?
  
• Could this be the valve cover gasket issue - leak by gasket above/at cylinder 1 leading to oil on that cylinder/plug top - but if so why didn't new plug in cyl 1 solve it with the coil of cylinder 4 swapped there?
  
• Could this be fuel injector(s)? And if so how to test/id. bad injector? And that would be unrelated to oil residue issue which I seem to have via one of the above mechisms?

Still got shudder and shake after swapping cylinder 1 new ngk plug, Then coil from cyl. 4 swapped with cyl. 1. No improvement. Odd thing is all the codes i kept getting - none included P0304 - even though I put the former Cyl. 1 coil onto Cyl. 4 and 4 (presumably good) onto 1.?

Also of note - shudder and shake is pronounced at low rpms/foot off gas in park. If i depress accelerator or put it in drive/apply brake and depress accelerator - the car shakes less/revs a bit. and if I put it in neutral it seems to idle smoothly. Also there is a pronounced chunk/shake when I put it in and out of Park from Neutral - so when it goes to charge it really shudders. I monitored on dr. prius and it's def. charging the hybrid battery which has good green bars/voltages/deltas.

Thanks for any thoughts - diagnostic tips. I have dr. prius and torque to look more in depth. Do i need a techstream type reader? any way to eliminate fuel injectors? Could it be MAF or throttle body/oil down inside there/pcv valve? And how do i eliminate plug- vs coil - vs injector vs. pcv vs intake/MAF ?

 

Found this thread and the last post seems relevant about the little pool of oil below/at bottom of throttle body plate - so I"m going to look at this angle a bit more. The problem is I haven't changed the oil recently - but will double check my oil level - but perhaps oil is my problem but it is from valve cover gasket leak or somehow pcv valve (since i do see small puddle of oil down below throttle body).

Post 28 - last post as of now -
Random Multiple Cylinder Misfire? | Page 2 | PriusChat

"From Howard K - ....Apparently the owners manual says to check the oil when the engine oil is at operating temperature. I had checked it while cold, and it was jus a little over filled. So, I drained it just below full line, changed the plugs and cranked it up. I checked it when hot, and it was way over the full line. The design of this engine has the pcv valve at the lower back part of the valve cover. Any overfilling will cause oil to be sucked into the pcv valve and straight into the intake, where it gets sucked straight into your engine, oil fouling the spark plugs. To prove this is happening, take you air filter box off and open the throttle by hand. Use a flashlight and look down into the intake. You will see a large puddle of oil. There should be no oil at all. This oil has to be removed, the spark plugs either cleaned, or changed. The oil level cold should be drained to about 1/2 way between bottom and full mark. Then crank up vehicle and drive it until engine is hot, then rechecked and filled about an eighth of an inch below full. The problem with the whole thing is that your car takes 3.7 quarts of oil, not 4. Most oil change places have an automatic oil dispenser. You dial in the number of quarts. They don't have fractions of quarts, they either have 3, or four quarts. Ok this being said, if you drain the oil, it is physically impossible to drain all of the oil out of an engine, there is always oil in the pump and oil galleys and lifters, etc. Sooo, if it has a maximum oil fill of 3.7 quarts when the engine is completely dry at the factory, and you put in 4 plus the residual oil, you have this exact problem every time. I am not debating this! This is very common in these cars, even the dealers do this a lot of times. Peace, love and hippie flowers. I hope this helps out a lot of people! #28 HowardK, Apr 9, 2022 "

 

Update - cleaned throttle body and MAF sensor with throttle body cleaner, and separate MAF cleaner respectively.

Marked the 4 coils and switched them around.

Started car with the possibly "good" cyl 4 coil into the cyl. 2, and cyl 2 coil in cyl 4.
still had shudder but diff. codes - instead of P0300 P0301 P0302 P0303
I got only p0300 0301 and 0303 - NOT 0302 OR 0304 (with cyl 2 coil in it).

strange. Could there be some underlying voltage/control issue 'firing' the coils/plugs that is out of whack due to a sensor/system that is off line/failed?

Any ideas/suggestions on a more enhanced code reader, or tech stream, or scope I could get that might let me see voltages/performance of indiv. coils, spark plugs, fuel/ injector info? Torque pro seems to have an air-fuel ratio reading - are there any individual or system wide fuel injector/flow rate readings I can monitor to tell me anything about why cylinders aren't firing?

Thanks so much for any troubleshooting ideas.

 

Ok, thanks MC, makes sense. Not sure the coils have ever been replaced.

For the coils - should I go with Toyota/Denso - or are there any equivalent OEM that are high quality but not as expensive?

 

Ok good news - got it fixed!

So it was the coils - or at least 2 coils.

After cleaning top of valve cover of scummy oily deposits, cleaning MAF sensor with MAF cleaner, and throttle body plate with throttle body cleaner, putting in 4 new ngk ifr5T11 iridium spark plugs and rotating the coils 1-4 through each position I still had misfire - but least bad with coil 4 on cyl 1 and coils 1-3 moved over one position to the right. I had encountered oil down in the spark plug well for cylinder 1 and a fouled plug - or I thought it was oil - but maybe it was oily water actually. One night during this troubleshooting I had all 4 coils inside after doing resistance testing, to try and find a 'culprit' - and when I came out to car in a.m. after a rainy night I found all four spark plug wells full of water! Doh. the windshield plastic cowl/drain gutter was plugged where drainage was supposed to pass through the metal fire wall even though I had enlarged this opening in the metal years ago. (am going to put a little mesh drain guard inside here to allow it to flow even if some leaf debris comes down inside - so it can't just block the drain). So had to suction water out of all 4 spark plug wells and dry with cloth down inside and gentle screwdriver swabbing around the plugs and aired it out. So even though I'd solved that windshield drainage problem years ago it re-plugged and I didn't see/figure that out until all the water spilled over onto the valve cover/cylinder tops. argh! This was a further clue to my solution I hoped. (vs. oil through gasket or fuel injectors, etc. that I didn't want to have to tackle ).

in these final coil positions I only got a P0304 misfire code for cyl. 4/coil 3 - even though I would have thought coil 1 would have been bad since it was in the most fouled spark plug well/on fouled plug 1 which had dark ring of oil/corrosion on it when removed. Other plugs were replaced but didn't look as bad.

So I bought new Denso coils from rock auto $57 each. At first I replaced coils 1 and 3 - which were in cylinders 2 and 4 at this point - cylinder 4 /coil 3 had the P0304 error and coil 1 cyl 2 - was from most fouled plug/cylinder location.

And bingo - smooth engine operation, no misfires, no codes, no issues. Drove it around a bit.

One thing I noticed was the new coils boots gripped the top of spark plugs much more firmly when installing into position - really snug - as I pushed them down into place. I'll keep coils 2 and 4 as backups - wonder if they're almost as good as new ones- but no way to test? assume they've degraded and I'll replace them even though engine runs smooth with them in.

Excited I won't need to learn the fuel injector replacement or valve cover gasket replacement procedures at this time.

Thanks for the advice and help all.