On Halloween, the check engine light on my 2007 Honda Odyssey EX started flashing. Read the codes which were a random misfire and misfires on 2,4,5, and 6 (P0300, P0302, P0304, P0305, and P0306 respectively). Symptoms were rough idle, no loss to power. The car is at 117k miles, we had just bought it a month earlier, so I replaced the spark plugs since I did not know when the were last replaced. In so doing, I found that the coil pack well (I think that is what it is called) for cylinder 5 (front-center) contained oil. The rubber boot on the bottom of the coil pack had swelled as a result and was stuck in the well on the plug. I eventually got it out, changed the plugs, put it all back together, but it was still misfiring. Took it to a shop that replaced the coil pack in cylinder 4 (front-left) and informed me that the valve cover seal needed to be replaced, not now, but within a few months (I am never going there again). Things were fine for a week, then the codes were thrown again (not sure what the new codes are, assuming them to be the same until I can get them read tomorrow).
Really rough idle until warm then not so bad, flashing check engine light while under load or stopped, then steady or off while coasting. Changed the valve cover seal on Saturday. Still rough idle, not as rough, but still rough (gets better the more it is ran), with the light doing the same as mentioned before. The rubber boot for cylinder 5 is again stuck in the well (couldn't get it out this time) with the rubber boot for cylinder 6 (front-right) missing altogether (it was there when it was taken to the shop, again, not going back).
I'm pretty sure it is a coil pack that needs to be replaced but I am not sure how to check which one. I'm thinking that it might be the one in cylinder 5 just because that is the one with the oil in it (couldn't get it all out because the boot was stuck), but I'm also thinking that it could be the one in 6 because it doesn't have the boot and so it is not making a good connection to the plug.