High Mileage Rough Idle

I have an ‘09 Prius with 405k miles. She’s been an absolute workhorse but she is throwing p0300, p0301, p0302 codes. It started as just p0301 and then I tried a bunch of things and now it’s throwing the p0302 as well. When driving under normal circumstances, it sounds great. However, when I first start the car up, I have a rough idle. Also, when I’m sitting at a stop light running on the battery for let’s say a minute, when the engine kicks back on, the rough idle pops back up for 10-15 seconds.


So far I’ve tried:
Swapping spark plugs
Swapped Coil 1 with coil 2
Cleaning PCV Valve thoroughly with carburetor spray
Thoroughly cleaned throttle body
Put some gumout in my tank thinking it could be the fuel injector(s)

Could it be that one of the fuel injectors is failing given the high miles? Specifically, could one of the fuel injectors be flooding the engine while stopped? Could I just have a leak causing a small amount of oil or coolant to get in while sitting? Could it be that I need to swap out the throttle body because it’s getting stuck at low rpms?

Any help would be greatly appreciated.

 

I have not. Do you think the symptoms seem consistent with that?

I haven’t logged P0011 or P0012 but I was just reading up on it and it seems that sometimes wouldn’t throw a code. The only other thing I was thinking is that I didn’t lubricate the throttle body after cleaning. Could that have something to do with it?

 

That looks pretty brave given my limited engine knowledge. I managed to clean the vvt screen and valve with some carb cleaner. The screen wasn’t horrible but certainly had some oil. Unfortunately, the issue is still ongoing. One update though is that I’m no longer getting a cylinder misfire after driving ~400 miles and using some b-12 chemtool. Oddly, my inverter coolant pump gave out on me about 300 miles in but I managed to get home ok. Before realizing my misfire codes had gone away, I put a higher concentration of high mileage seafoam in my tank having read that a higher concentration can help (2 oz/ gallon).

How would I go about getting cam timing readings in inspection mode? I managed to get into inspection mode and hookup my Bluetooth scanner and created a few screenshots from live readings in car scanner. I’m not sure if this tells you anything but I’ve attached them for your reference. I really appreciate your help.

 

IMG_5217 by 400kclub posted Jun 18, 2021 at 9:17 PM

IMG_5219 by 400kclub posted Jun 18, 2021 at 9:17 PM

IMG_5220 by 400kclub posted Jun 18, 2021 at 9:17 PM

IMG_5221 by 400kclub posted Jun 18, 2021 at 9:17 PM

IMG_5222 by 400kclub posted Jun 18, 2021 at 9:17 PM

IMG_5223 by 400kclub posted Jun 18, 2021 at 9:17 PM

IMG_5224 by 400kclub posted Jun 18, 2021 at 9:17 PM

 

I'm not super knowledgable when it comes to engines though its certainly become more of an interest as a result of these recent issues so apologies in advance if I'm a little slow. After looking through some screenshots I saved while in inspection mode, I noticed a reading of 10 degrees which was listed as "timing advance" in the car scanner tool I'm using. I noticed that this increased to 14 degrees once the engine started charging the battery. Does that help provide any information? If not, could you help point me in the right direction?

IMG_5219 by 400kclub posted Jun 18, 2021 at 9:17 PM

 

Doesn’t the vehicle do that automatically when the 12v battery is disconnected?

 

I didn't clean out all the oil in the intake because at the time, I was concerned about removing the throttle body completely when cleaning because of leaking coolant, etc. Could that cause my symptoms?

Today, I ordered a set of rebuilt oem fuel injectors to see if replacing them might help. My Prius hasn't thrown a code for a misfire in a while but I did notice a count of 7 misfires in cylinder 1 in the noncontinuous monitor. Is it possible that injector 1 is getting stuck slightly open due to carbon buildup and slowly flooding the cylinder when it cycles off? It's just interesting how when I start the engine cold, it rarely has the idle issue, it occurs when the engine cycles back on to charge the battery after it's been sitting a couple minutes in park or at a stoplight.

 

Update. A few days ago, I swapped out the water pump which fixed the p0A93 code. The following day, I got another coolant temp warning light so I checked an my engine temp was up to 245 so I checked and my coolant was pretty low. It’s possible I lost some coolant while replacing the pump or perhaps I have a slow leak and hadn’t stayed up on it.

Today, my fuel injectors came in the mail and I successfully installed them (to my surprise) but, sadly, I’m still having the same issue. Afterwards, recalling your post above, I removed the TB, pinched the lines (messier than I was expecting) and cleaned the remaining oil from the intake. Still the same issue. The only thing I haven’t done (because I feel like I’m over my head) is to clean the intake ports and to check the vvt selenoid with the 12v to see if it actuates quickly. I should mention that I have had the the p0420 failed cat code for about 150k miles. Not sure if it could be causing some sort of exhaust issue given the high miles. Any thoughts or recommendations?

Thanks so much for your help!

 

I was referring to the inverter coolant pump. Do you have any recommendations for the rough idle issue/ cylinder 1 misfire?

Could my symptoms be consistent with a damaged throttle body

I know a guy who has a fleet of Gen 2 Pri and 2 of them have failed engines and both made it to 600k miles. He also told me that his cars burned through so much oil that you never have to do an oil change so I also don’t think he was super careful with maintenance.

 

Just in case this helps someone else out in a similar situation: It appears that a small, coolant leak can form in the head gasket at cylinder 1 around 400k miles in Gen 2. This will eventually cause misfires. After driving it more, my symptoms became eerily similar to another post.
Is it really an internal coolant leak? | PriusChat

I used Bar’s Block Seal Liquid Copper which can be used as a temporary measure to try to stop the leak. So far, the behavior has stopped and it’s been a couple days.

I have read that the main ingredient in this Bar’s formulation, sodium silicate is some pretty powerful stuff which hardens to a rock when heated to above 120 degrees c and there are instances of people driving for years with gasket issues. It’s also known for killing engines when put in crank cases so don’t use it with any old coolant leak. Apparently, it was once used to destroy tank engines.

I will update the forum with updates on how it works for me but thanks for everyone’s help.