Non-typical engine shudder cold or hot - no error codes

Hello, I'm having a problem with my 2013 Prius v Five with 147k miles.

Long ago (around the 100k mark) about every 50 or so cold starts the engine would shudder violently for 5 to 10 seconds and then smooth out. Slowly over time the violent shudders increased in frequency to about 1 in 10 cold starts. But last night, with the engine fully warmed up in 60 degree dry weather, after driving for about an hour the engine started to vibrate violently in stop and go city traffic, whenever the engine would turn on from all electric mode. I temporarily solved it by putting the gear selector in "B" mode so the engine stopped shutting off and the shudder did not occur for the remainder of the trip.

Since the shuddering started about 50k miles ago, I have had to add about a 1/2 gallon of coolant. However there is no noticeable white smoke from the tailpipe and no noticeable moisture in the oil, but could a blown head gasket still be a possibility?

Also, as far as I know the EGR has never been cleaned.

Looking at this forum it looks like the problem could be any one of about a dozen things from a dirty EGR, to a dirty PCV, to a dirty MAF sensor, to the wrong octane gas (I typically just use Shell 87), to water in the gas, to coolant needing a flush and fill, to a bad water pump, to a bad motor mount, to failing coil, to a fouled plug, to a bad coil wire, to a to blown head gasket!

Can anyone recommend the diagnostic steps you would begin and follow with in my situation?

 

Thank you for the responses. Definitely not what I was wanting to hear. But it is a bit confusing. Why would the engine shudder repeatedly going from electric to engine after the engine was fully warmed up and not produce any smoke whatsoever if it is the head gasket? And if it is the head gasket why when I went to start it up this morning there was no shudder and as usual no smoke? It almost seems like an electrical malfunction to be this random. But if it was I suppose it would produce a code, but as yet, no light on the dash and no codes when I read the OBD with the Torque app.

 

Thanks, I'll give it a try...

 

I am not up to doing a head gasket myself. I have been calling around local shops and no one wants to touch the Prius hybrid engine except Toyota dealerships! I'm waiting to hear back from service managers at two dealers, but so far one dealer quoted me a price of $4,200! They said it is a 20 hour job.

Can anyone recommend a shop in the Central-Maryland / DC / South-Central PA area?

Or maybe I should look a rebuilt engine?

 

Thanks all for the advice. I decided to go with a JDM engine from eBay that has less than half the miles of my 147k engine. It was just delivered today and it looks nice with one exception: the flywheel has some light surface rust (perhaps got rained on?). If this thing was left out in the rain will that cause any problems? Should I put my old non-rusty flywheel onto the new engine?