P0300, P0303, P0304

I have a 2008 2nd gen Prius with 146K miles. Over the last few cold mornings I noticed the engine was running rough on start up and finally today it tripped P0300, P0303, P0304 indicating misfire on cylinders 3 and 4.

History: My son took the car this summer and spent the summer doing mountain driving out West. He did lots of engine braking as he would come down the mountains. As a result, the car consumed 2.5 quarts of oil over a couple of months. The car has never used any oil and the engine braking is the most logical explanation. When I got the car back, it stopped using oil.

What I think is going on is that all the oil that was sucked back into the intake has fouled the plugs, MAF sensor, and the throttle body / plate.

Here is what I will do and I will report back with the outcome.

1) clean the throttle body / plate
2) clean the MAF sensor
3) replace the spark plugs
4) replace the PCV valve

If 1) - 4) don't solve it, I will move on to vacuum leaks, coil packs, and injectors.

Questions:
For Gen2 do you need to remove and clean the intake manifold (similar to Gen3)?
The Gen2 has no EGR and therefore no EGR passage ways that get clogged, correct?

Thanks for your input and advice!

Mark

 

Done with changing the spark plugs, PCV valve, and cleaning the throttle body / plate and MAF sensor. I did notice oil puddled in the intake manifold. I broke it up with the throttle body cleaner and extracted it. The plugs did not look pretty and both plug threads and the PCV valve was coated in oil (see attached photos).

It had to be the plugs. I checked the gap and all four were at 0.060+. The recommended gap is 0.043. I assume the oil in the intake and its burn off prematurely eroded the spark plug electrodes. These plugs only had been used 22K (changed at 124K, current mileage is 146K).

About this ... The car had never used any oil between changes and so my son never checked it. When coming back from out West driving in rolling hills, the red triangle flashed briefly. He immediately stopped, Googled, and determined it was low on oil. No harm was done. When the oil was changed there was no evidence of degradation.

The car runs very smoothly now. If the problem returns, I will post in this thread.

Thank you everyone for your input and comments,

Mark

 

I now suspect these plugs were fakes since they only lasted 22K miles. Note that the "iridium" tip is totally gone in the photos. From now on, nothing but legitimate Toyota dealer parts departments for parts. I will buy from
Authentic Toyota Parts | Toyota Parts Overstock
or equivalent. This is not the first time I have had to deal with fake parts and you think I would learn the first time :-(