Cyl 1 misfire...what to ?

probably the egr circuit, but could be plug, coil or injector. you can swap things around in a process of elimination.
how many miles on her?

 

That would be kind of a shotgun approach when there is a misfire in one cylinder being reported.

The big three usual suspects in a misfire are fuel/mixture, spark, and compression. There are ways to systematically work up each of those and see where the trouble is.

A leakdown test is a good way to check the compression situation. If there is a cylinder not holding compression well, you are also often able to hear what kind of a leak is involved. If you have a borescope that can look in the spark plug holes (the plugs need to be removed for the leakdown test anyway), you might see whether anything about cylinder 1 looks noticeably different from cylinder 2.

After comparing the condition of the removed spark plugs, if you saw no differences there, you could reinstall them so the original no. 1 was swapped with one of the others, and see if the misfire moves around. A similar strategy is possible with injectors.

Misfiring under some conditions can be caused by unequal clogging of four small passages in the intake manifold, and those are worth checking because the car's ECM could tell you if they were all severely clogged, but it can't tell you if they're unequally clogged. That's easy to see by taking the manifold off and looking.

Things like injectors and igniters are pricey enough (for OEM) that it's not very appealing to wholesale replace them all just to shotgun a one-cylinder problem. You can find aftermarket sets for much less money, but that begs the question whether it's worth replacing a whole set of probably-fine OEM ones with possibly-inferior aftermarket ones, just as a way to shotgun one problem that might be something else entirely.

There was a recent thread here where somebody replaced all the igniters with so-called "Toyota" ones being sold on ebay, and those repeatedly blew fuses and stranded him until the old good ones were put back in.

 

Ok after a warmup and subsequent ICE cycles often leads to a head gasket on 2010-2014 Prii. Does not matter if the coolant reservoir seems ok and will rarely have coolant in the oil. Diagnosing makes sense, the "easier" parts cannon will just cost you more in the long run. Obviously you have a borescope or leakdown test run to confirm. Not a compression test. Egr will likely be clogged and will need attention during the repair, but clogged egrs don't cause these classic Prii hg symptoms.

Or you can wait and see if it gets worse.

By the way, Block Sealer often lasts a few thousand miles and will often completely mask the issue.