The car has been running great*. Last night out with friends, hop on the highway and give the car maybe 1/4-1/3 throttle. As soon as I do the check engine light comes on and the car runs a bit rough and is down on acceleration (not that I am into the throttle at this point). Get to a point where I can stop and pull the cars - code 300, 301, and Random Misfires. So if I remember correctly code 300 is misfire cylinder 1 and 301 is misfire cylinder 5.

When I restart the it seems fine, a couple of revs and it seems like its normal self. When I drive home a couple of hours later the car seems 95%. Although I am now driving like a grandma.

The plugs have maybe 20k miles on them.

The astrix up top is that while the car is running I do suspect a leaking IC that I am in the process of addressing. I popped the hood and did not smell any coolant or see anything amiss.

Any thoughts why I would suddenly throw these codes and what to check? My first thought was the IC leak getting pretty bad but the coolant did not drop noticeable and if there was no smell of coolant.