Error Code P0303 After Oil Change

It is possible the 3/4 to 1 quart oil overfill forced liquid oil through the pcv system into the intake manifold.

Don't waste money and time on ignition coils or plugs before you check out the most common issues.

1. Does it continue to shake and rattle after the initial start and warmup? Or does it run pretty good?

2. Is this the very first time for a rough rattling start?

3. Does it idle poorly and try to stall? Obviously with the engine running.

 

So why do you think there's a problem with coils or plugs, when it only does it on cold start-ups????
Check and mark ICE coolant level, see if it slowly goes down.....

Good Luck.........

 

You certainly have misfires but not coil, plug or injector based. Not when it clears quickly and runs fine. In fact you may go days or weeks before it repeats which often fools mechanics into thinking the $500 - $1000 with of replacements actually did something.

Answers 1 and 2 point to an early onset small head gasket leak. Borescope inspection is the only definitive test at this point.

Answer 3 suggests it's not an egr valve stuck open and certainly not a clogged egr cooler causing misfires. But a block egr flow test can prove it.

Car Care Nut HG Borescope at 660s

Excellent Borescope Footage at 6:50
Honda Misfires on Coldstart Only

Egr block flow test

At about 10:15 in the video he starts talking about the egr valve letting "air" into the intake manifold. He means exhaust gasses.

 

You bought it in March of this year, with 204k miles (currently at 210k), saying seller had fixed head gasket and cleaned EGR. I’d wonder how and when he did both.

New Buyer/New User - I'm Wary and Cautious... | PriusChat

 

Ah the sweet innocence of youth. A flashy body and a warm interior sucks in many a young man.

A can of head gasket stop leak "fixes" it - for a couple of months. Welcome to the gen3 repeat offender club. It's a small group but not that exclusive anymore.

Now that the bloom is off the rose you can see the thorns.

I will say Ms V does have a very good body and she cleans up well creating a very good first impression. It's not her fault, her handler probably was not very good to her and dumped her for a younger model.

 

That is normal in early stages on a Prius gen3.

 

Well if it only happens 75% of the time - that means it's only 75% broke. Run it until you can get the last 25% out of it. Don't worry about it leaving you stranded somewhere - key in banjo music. Have you ever seen Deliverance or those slasher movies where someone is stranded on the side of a lonely road out of cell service range?

Sorry, in a corny mood - Denial isn't just a river in Egypt......

 

No it won't go away. Running the diagnostics listed above is the best approach.

Driving it as is means you are risking a blown engine. Bent connecting rod, sometimes a hole in the block.

Often sleazy sellers clean up an otherwise clean car and dump stop leak into it to stop the rattle for a month or two. They give you a tail light warranty, eg they sell the car as is with no warranty.

Most pro shops and dealers do not recommend a simple head gasket replacement. They usually recommend a rebuilt engine.

 

After a quick glance at that spreadsheet - I would've took that car for free. Definitely wouldn't pay any money for it.
Just look at the various oils being used for oil changes and crappy filters being used - tells the entire story. It's a fairy tale with a very bad ending. The only reason to place heavy oil into the car is to slow an oil consumption issue. Using 15w50 and/or 15w40 in an engine that suppose to use 0w20 is NOT good.

 

Yikes!

 

Don't know what the previous owner was thinking. He probably has a brain worm too.
It could've just been stupidity - old race car drivers or truckers use those oils so it must be better for my car?????
The car burns a lot of oil so putting in thicker oil will slow down the oil consumption.
That's all speculation on my part............

I know that putting thick oil like that will prematurely wear-out your engine. When an engine starts up, it's kinda like a 'dry' startup since the oil pump starts tuning and pushes oil to the critical area of the motor to prevent wear. Imagine replacing the oil with molasses - it's going to take a LOT longer for oil to get to where it needs to be, considering the engineers designed the motor for 0w20 with smaller oil passages and tighter tolerances than an old diesel motor. Add to that, the Prius is an auto start-stop motor that turns itself on and off as needed - so much more start-stop cycles than a regular motor = more wear and oil starvation.

 

If it was set up as a hot running pure ICE race engine with looser tolerances for reduced friction, maybe. But not in this case.

What's additionally odd is how quickly the oil changes went from OEM 0W20 light to 10W30/15W30/15W40/15W50, heavier and heavier.

 

Race engines also gets torn-down and rebuilt every few thousand miles too..... They're pretty much experimental motors, real life wear and tear to see how different components and formulations work as predicted. Thinner oils was first tested on the race tracks.

 

No.

The gen3 engines from 2010-mid 2014 have low tension rings. This combined with the first ever Toyota recommendation of 10,000 mile oil changes caused a lot of excessive oil burners.

A good engine can go 5,000 miles without any observable oil loss. However some oil dilution still occurs from blowby and condensation so 5k changes WHEN THE ENGINE IS VERY GOOD is the magic bullet along with 50k or less coolant changes.

98% your guy was trying to stop or slow down oil burning but thicker oils did not help this problem. What thicker oils can do is screwup tight tolerance engine parts like the variable valve timing. However timing is not usually impacted. The ONLY fix for excessive oil burning (one quart per 1200 miles which is way excessive) is a rebuilt engine with updated pistons and rings.

As a side note a rebuilt engine with parts Toyota improved for this problem child includes rings, pistons, head gasket, intake manifold, egr valve and engine control software.

Parts you don't EVER want are aftermarket water pumps, injectors or coils. You never want to add r134 refrigerant that has oil or stop leak since this is a special electric compressor that runs on high voltage. Normally you don't want "oem" Toyota parts off ebay or Amazon as they are usually cheap counterfeits with fake Toyota packaging.

Best solution to another head gasket in this case? Buy a Hybrid Pit rebuilt engine and have it shipped to you or your mechanic. Low cost solution? Buy a JDM used in Japan engine from a distributor in any big city. Some get lucky and get a JDM that was built from 2015-2021 and end up with a solid gen3 engine.