Shaking when ICE accelerating

Hello,

My father has a 2012 Plug in. This morning he had to turn around and come home because he said the car was shaking when he accelerated enough for the ICE to kick in. He noticed right away that putting it back in EV mode made it stop. We took it around the block just now and also noticed that even with the ICE on it doesn't start to shake until you try to accelerate a little bit, or trying to maintain speed up a moderately steep hill.

I did some reading here which made me concerned about the head gasket possibly leaking, but my father said he looked at the fluids a couple weeks ago, and right now the coolant isn't low, and doesn't look any lower than it did then.

The car has a little under 90k miles. It gets driven regularly but not very far. At least once a week it goes on the highway so the ICE would be running. He says in the summer it might go 6 weeks between gas fill ups at the most. The check engine light is on but not flashing.

My father ordered a cheap port reader online before I talked to him, so I don't think it is one that can read Prius specific codes. He wants to wait until it gets here before doing anything else.

Anything else we can look at in the mean time?

 

The reader shows P0301. Yesterday he put a bottle of Sea Foam in a half full tank then topped off the tank. This morning the ICE started and apparently was running normally and the check engine light even turned off, but at some point not long after leaving it started to shake and rattle worse than before. He got it back on the battery and charged it afterward, then tried the ICE again later and the same thing happened. The check engine light was flashing instead as well.

Still no change in coolant levels, but the gas engine just hasn't been run very much so I can't say with any conviction that I doubt it's the head gasket.

I might give cleaning the EGR / intake a go based on some videos I found linked here, but it's more of a job than I initially thought so I'll have to check if I have hose clamps etc.

Unless anyone has better suggestions.

 

We decided to change the spark plugs first as it seemed a bit easier than going after the intake manifold / EGR system and having to deal with disconnecting coolant lines.

I found out that the discoloration around the edge of the ceramic indicates something called blow-by, meaning the spark plug is leaking. All 4 of them were like this. We also learned that at some point Toyota changed the spark plugs for the Prius, I think to one that is a little hotter, so these were replaced with the updated spec plugs.

We couldn't get it to knock again starting it in the garage, and even took it around the block quickly (because it's snowing and the wipers were off the car still). So we decided to put everything back together and take it to get groceries, about 8.5 miles round trip, and kept it in power mode with the fan on etc. so the engine ran, and it ran as smooth as can be and no check engine light.

Here's hoping this was the problem. I think cleaning the intake manifold and EGR soon is still a good idea. The car has almost 90,000 miles but since it's a plug in and because of how it's driven the majority of that is on battery we think.

 

Forgot to mention I rotated all the coils. It's not the tips of the plugs but the discoloration on the ceramic above the threads. I read that means the plug is leaking.

I think for now we are going to wait and drive it some and see if it starts knocking again. Hopefully this isn't pushing our luck because it's due for inspection next month.

 

I appreciate the advice and the links. It sounds like the decision has been made here to get rid of the car already though.

For what it's worth, I just saw a video from a Toyota mechanic about how to look for a head gasket leak without special tools, and they showed how coolant can wash off the residue on a spark plug, and our car doesn't have that at all. I'd be interested in doing the test they did where you hold paper over the cylinders and crank the engine with no plugs in to see if coolant splashes up on the paper, but it doesn't seem like any more work will get done on this car by me.