Occasional Jerking/Shuddering, Lumpy/Rough Idling Engine

Hi Priuschat,

I've been noticing some shuddering/jerking from my Gen 2 recently and am not too sure what to make it of it. Symptoms are:
- A bit of shaking through the steering wheel and seat (but no audible noise) on what seem to be mostly random occasions so far - right after starting (sitting idle), at low speed, and when the engine turns off when sitting at a light. It's not very consistent though, I'm still trying to figure out what the pattern is. No problems while turning though, so it doesn't seem to be my CV axle (which does have a torn boot I've been concerned about).
- Most alarming is that twice now on the highway the CEL light was *flashing* for maybe a minute before going away. I checked the OBD2 codes later on, but the only code was P0420 (which I've always had since installing my aftermarket catalytic converter). So I don't know what the flashing was indicating exactly, but my guess from what I've read is that it could be some intermittent engine misfiring? Is there any way I can confirm this if it didn't set an engine code? Is there compression data I can check via the OBD2? Maybe check the RPMs?

My Gen 2 is at about 105k so I'm thinking my spark plugs are going out early and I should replace them now rather than wait for 120k. But it sounds like there could be a number of other causes: coils, injectors, dirty PCV, dirty MAF, or even engine mounts, clogged cat, unbalanced tire, etc. so I thought I'd check here before I start doing work on it. (My engine oil and coolant levels look fine btw) Any suggestions for how I can diagnose further? Would it be a bad idea to keep driving as-is and just wait for an engine code to set?

 

So I checked the oil level after the first flashing CEL, but it was at the top fill mark and looked pretty clean (had it changed <1500 mi ago) FWIW.

I haven't had any issues with losing oil between changes and do check the oil level/color from time to time (maybe every third fillup). Hoping it's not engine damage :/

Re: shuddering at red lights, I think that's probably happened before all of this; I may just be more aware of it right now trying to figure out when this shaking tends to happen.

Biggest safety risk at this point seems like possible hesitation when accelerating. I do sometimes notice a bit of hesitation (accelerating from a stop) along with the traction control light coming on, but that may be something else (will get alignment checked).

EDIT: Side note, I did also just slightly overinflate my tires to 41 front / 39 rear per other threads. I may just be feeling a lot more of the road right now as well, but it's the flashing CEL that has me most concerned right now. I felt shaking sitting at idle too, so that rules out this being a tire issue.

It's a bit baffling to me that the engine would misfire but apparently not long enough to log a code... Would setting up Techstream be useful here?

Reading this I wonder if I might have bad fuel injectors, maybe they got damaged since I have run the tank low (to flashing) before: https://www.vehicleservicepros.com/service-repair/underhood/article/21029342/attacking-no-code-misfires Maybe a little fuel injector cleaner would be worth a try?

 

I guess the problem isn't occurring often enough to worry too much about yet (was fine today), and it's intermittent enough that bringing it to a shop probably wouldn't be much help either. For now, I'm thinking I may try using some Techron to ensure the fuel injectors are clean (if that's safe for the fuel bladder) and also clean the MAF, as a first step.

If things get worse/consistent, I'll replace spark plugs, coils, PCV as one job (seems to be a good idea at 100k anyway) and maybe also clean the throttle body and intake manifold too.

Also possible my aftermarket cat has clogged up after a year; it's always thrown occasional P0420 codes though (figured just low efficiency, not clogged): Amazon.com: Customer reviews: AUTOSAVER88 Catalytic Converter Compatible with 2004-2009 Toyota Prius 1.5L Direct-Fit (EPA Compliant). I guess I can check the temps via an infrared thermometer rather than try to do an exhaust backpressure test?

 

Just confirmed misfiring, I got a P0301 code set just now after a few CEL flashes.

Will probably change the plugs this weekend, thinking maybe some Amazon iridium ones will do:

Or is it best to go OEM for these, just in case of counterfeits? May try RockAuto: 2007 TOYOTA PRIUS 1.5L L4 ELECTRIC/GAS Spark Plug / Coil-On-Plug Boot | RockAuto Found that the Toyota manual recommends: Spark plug type: DENSO SK16R11 NGK IFR5A11 Spark plug gap, mm (in.): 1.1 (0.043)

I guess I may as well change the COP boots while i'm at it? More Information for STANDARD MOTOR PRODUCTS CPBK624

 

Sadly I broke the 10mm aluminum bolt on the second coil packs while torquing it to what I thought was 10ft-lb... I was able to remove the two pieces but not sure what to do now.

Is there any donor bolt I could take from somewhere else on the car? Any idea if it's a standard size I could order? I had I feeling I shouldn't have trusted the uncalibrated torque wrench I just got (goes up to 80ftlb max).

 

The relay box and other screws I found around the car were all a bit too shallow. I ended up digging up an IKEA bolt that seemed to be the same thread pattern (presumably some M* pattern). I tied a zip-tie under the head to shorten the effective length and it seemed to torque in just fine at that point; coil pack was as snug as the other 3. I was afraid of the plastic melting under heat, but the coil pack head and connectors are all plastic adjacent to that bolt, so I'm not sure that will be a problem. Will probably go buy a proper replacement bolt (or a set of metric bolts) but this seems to be working after a brief test.

Spark plugs were definitely the culprit. Engine runs nice and smooth now. Old spark plugs had corrosion (white residue) all on the electrodes and green corrosion at the hex base (will post a picture later). Maybe they would have benefitted from dielectric grease (not sure Toyota does that from the factory). Hoping I'll see an MPG increase. (I did end up getting OEM Denso plugs)

Boots looked like they were in nice shape and I saw no cracking so I left them as-is.

I'm thinking I may go ahead and get my oil changed now even though it's only been 3.5 mo and ~1600mi, since I've been told unburnt fuel could have gotten into the crankcase and contaminated the oil. It's only been intermittently misfiring for less than two weeks (drove probably <100 mi like this and <20mi since the P0301/P0302 code set) though; am I overthinking this? The amount of unburnt fuel in the oil might just be negligible. My MPG didn't seem to drop significantly during all this either.

 

I think I'll end up going back in with a proper 20-200 in-lb torque wrench and then make sure the spark plugs are right at 13ft-lb. Reading some scary stuff about the potential consequences of under/over-torquing spark plugs and realizing now I've underestimated the importance of precise torque (not just 'snug' + 1/16 turn like I've seen online). Also wondering now if the use of socket adapters (I had to adapt tools I have in 1/4", 1/2", and 3/8" to get the job done) threw off the torque wrench that I did use (5ftlb-80ftlb)

 

Parking outside in WA where winters are constantly wet. I tend to make 15 minute drives too, so it sounds like those kinds of conditions.

I think the plugs I took out were the original ones that came with the car so they were beyond their life anyway; hoping even if fouling faster than normal that this new set can get me another 50k.

 

Hoping if I use a in-lb wrench I'll be in better shape (200 in-lb max) on a second go.

I heard about counterfeits. I bought mine from Amazon (direct, not third-party seller) and didn't see too many bad reviews:

I guess I could have been more patient and tried ordering direct from Denso/Toyota but was afraid continuing to drive with misfires would do more harm. I guess we'll see how long they last; 50k or even 30k is fine with me since I don't drive much.

 

Been about 150 miles on the new plugs and the engine has been nice and smooth, no misfiring or engine codes anymore.

But my MPG seems to be lower (about ~40mpg so far vs ~45 just before this). Possible symptom of counterfeit spark plugs? Or imprecise gapping? I didn't verify the gapping before I installed; they looked okay by eye but I didn't want to risk scratching the electrodes on this type of gauge: https://www.walmart.com/ip/Hyper-Tough-Steel-Spark-Plug-Gap-Gauge-Automotive-Tool-Model-4706/132932441?wmlspartner=wlpa&selectedSellerId=0&wl13=2385&adid=22222222277132932441_117755028669_12420145346&wmlspartner=wmtlabs&wl0=&wl1=g&wl2=c&wl3=501107745824&wl4=pla-293946777986&wl5=9033292&wl6=&wl7=&wl8=&wl9=pla&wl10=8175035&wl11=local&wl12=132932441&wl13=2385&veh=sem_LIA&gclid=CjwKCAjwuYWSBhByEiwAKd_n_sikZQZ5ndHTcHg8YKzGoevv9e1jqXWlPRSbbdelq87z1QXgsJI4ABoCJ3gQAvD_BwE&gclsrc=aw.ds

I went ahead and ordered some OEM spark plugs. Will try those and see if that helps. Will also retorque everything to spec with a new wrench, in case that helps.

I did also unplug the 12V after install to get the ECU to relearn the idle on the new plugs, if that matters here.