Stumble at idle post TB and Injector cleaning

Hi All!

My 06 Prius is up to 252,000 miles!

Last week I got in the Prius to go to work in the morning and it was idling really REALLY rough where it sounded like a jack hammer under the hood! I let it sit and eventually it stopped after warming up. After going through this in the morning for a few days after the car sat overnight, I finally got a check engine light: Cyl misfire 3, cyl misfire 4, general cyl misfire.

So, thinking the car has so much mileage, and I replaced plugs and coils back in April of 2020, I went and had the injectors cleaned and reinstalled. Prius ran even better, but still had an occasional shudder and rough idle for moments at a time.

I went and cleaned the TB in place with spray and rags and cleaned the MAF with MAF spray, put it all back together. Went for a spin and for the first 30 min it was idling high, then low, then high again. I parked it and pulled the black terminal on the starter battery for about 20 min...thinking it would clear the memory of the TB position?

After battery was hooked up, I reset the auto window and radio pre-sets....and the idle was now normal. Car ran really really well and I went and did and changed the oil (it was time). I thought I had it all resolved!!

I got in it this morning and it stumbled/shuddered again! very lightly, no engine lights, but still shudders!

Do I need a new MAF?

I'm hoping it is not a fuel pump....

Any advice?

 

Well, to update here (it's been a while) I ended up removing the throttle body, intake manifold and saw some CRAZY stuff in there: a coating of oily crud....black, sooty, and looked like tar! GROSS!!

Here's what I ended up doing:

-Firstly the throttle body was so cakes up with crud on the intake side that I went through a can of carb cleaner and scrubbed it all out... and it same out MINT!

-Secondly, I had the intake manifold SOAKING, stuffed with rags in brake cleaner to remove all of the soot and oil varnish that was build up in the runners!! Just kept spraying and scrubbing as deep into it as I could with brushes until, after 4 cans of brake cleaner, ALL of the aluminum inside was shiney and not coated and clean!

-Then I looked at the intake ports on the head and they were also cake sup with crud! I soaked a rag in gasoline and stuffed it in each port, then used a paint brush handle to try and remove as much of the oil residue crud from in there!!! I don't think I got all of it, but I'd say I got almost all of it!

I think I may need to install a catch can??

In the end it all went back together with new gaskets and and can ran pretty well after. Been through about 3 tanks of techron to hopefully get any of the crud I loosened up in the intake ports that didn't come out...and hopefully some of that worked it's way out. I still get stumble here and there...but it is 90% less frequent than what it was before I pulled everything apart. I'm hoping this is just any last remnants working themselves out? Any ideas on what this stumble could be?? Still no CEL's and it runs and drives well...get pretty good mileage for 250k+ (37-42 in stop and go...not much hwy driving in the past 3 months). I may replace the plugs just for the heck of it. The coil packs are about 6 or 7 months old.

 

Thanks for your responses guys!

I am going to look into the Torque app and the adaptor. What adaptor is needed? I only have a regular OBDII scan tool. I'd love to see what the values are and determine if the MAF is on the fritz.

Yes, all good calls and also what I thought. The shuddering is (IMO) definitely coming from the engine and it seems like a momentary loss of ignition...like a coil pack gets unplugged for .05 seconds. I will replace the plugs; they are cheap enough and it is easy to do. Coils are not even a year old, but I did not get them from Toyota...maybe the aftermarket coils are crappy?

No CEL's...I only had misfire codes when the stumbling was really bad but since I did the intense intake plenum cleaning no codes...

 

Forgot to mention...still have a stumble from time to time and id like to resolve it.

 

I've always used Castrol high mileage. Always at 3000 miles....sometimes 4000 when pressed for time.

So, do i understand it correctly that the blow by is what may well be causing the stumbles?

Guess if thats it, then its an engine teardown and new rings??

 

You know what....I'm an idiot...I didn't clean the damn hoses I didnt notice any gook coming out of them, but then again I didnt look....just disconnected and re-connected.

I guess that's the next step is seeing what it is like in there...

I got the car in Feb of 2018 with 192k just to commute and put on about 500+ miles per week for about 1 year. Once I got the car, I 9 changed plugs, oil and trans fluid and just drove it on 91 or 93 octane with an occasional Techron fuel system or injector treatment every few months. Currently at 253,000 miles.

 

sticky valve - Is there a check for this?

weak valve spring - Is there a check for this? I may well be pulling the valve cover off (see above responce to edthefox)

marginal compression - I could throw a tester on it, but when it iddles the car doesn't stumble consistently...just periodically. It does seem to happen more when the car is cold, but sometimes happens when warm.

weak ignition coil - the ignition coils I replaced with were not OEM...should I install OEM ones?

uneven injector flow or poor spray pattern - Had the injectors cleaned about 1.5 months ago, tested and new o-rings.

intake valve deposits (when you were cleaning, did you get all the carbon off the valves- down to bare metal?) - I tried all I could to get the valves cleaned but it was so hard to reach in there. They looked clean and without the oil residue crud from where I saw, but the opposite side I could not see.

ingesting a slug of pooled oil from the intake - Intake was cleaned out and used bout 4 cans of brake clean to get the inside of it back to silver aluminum....it was all black/tarred inside. I will check (once sun comes up) if there is still oil pooled up in the intake manifold.

 

Engine coolant has been stable the entire time. It seems a catch can for the PCV crud would be a good thing to install once this stumble is resolved.

 

Well...I just went outside, pulled the filter cover and opened the TB plate. Peeked in there with a flashlight and saw some golden colored oil pooled up in my nicely cleaned manifold....



Sure hope this isn't the end of my lil'Prius