Had to change out the head gasket, particularly on the bank with cylinders 4,5, and 6 (the front-most 3 cylinders). That process, while cumbersome, worked out fine. I had to get the front cylinder head machined, since it was low in one point by around 8 thousandths. Everything went back together relatively smoothly. Once done, the engine started up on the first try, and it ran smoothly.
And then, while making sure the coolant and other fluids were filled correctly, the engine died. It turned out that the auto tensioner pully’s bearings blew up, complete with ball bearings all over in the timing belt cover area. Luckily, the belt didn’t break, but as best as I can tell it jumped one or more teeth.
After redoing the timing belt, complete with a timing belt kit – just do yourself and your car a favor and buy a timing belt kit – the engine started up, but it ran pretty rough. The codes reported misfires, especially in cylinders 4 and 5 (the front left and center cylinders when viewing the engine from the front of the car). However, it also reported random cylinder misfires. It also reported the bank 2 sensor 2 oxygen sensor heater circuit was bad somehow (this is the O2 sensor on the bottom of the front three-way-prewarm-catalytic converter… something like that).
I replaced the bank 2 sensor 2 oxygen sensor, but that didn’t chnage anything. Then I started unplugging ignition coil plugs one at a time to see which cylinders were misfiring. Sure enough, it was cylinders 4 and 5. I got new spark plugs and new ignition coils (for all cylinders). That seemed to help a bit, but it was not all the way. The engine was still misfiring on cylinders 4 and 5 (wet spark plugs that smelled like fuel).
I did a compression test on cylinders 4 and 5 to see if the valves hit the pistons when the incident with the auto tensioner pulley happened. compression was fine – 130psi or so. It’s relatively easy to test this if you have the tool.
Then, I did the CKP sensor relearn procedure. That’s “CranKshaft Position” sensor. And it worked. No more misfires, and the engine idles smoothly now – more more rough idling, it now starts easily, and it doesn’t almost die at idle.
I didn’t have a tool that would reset anything, so here’s what I did (based on what the Honda service manual outlined):
Started the engine in the driveway from cold, and ran it at 3000RM until it got up to temperature. Drove it around in 2nd gear (automatic transmission), getting up to 2,500RPM and then letting it coast down to around 1,000RPM (keeping it in the same gear). I did this about 5 times in either 1st or 2nd gear. I then went on a larger road and ran it in 2nd gear up to 5,000RPM and then let it coast down to 3,000RPM (keeping it in 2nd gear). I did this around 3 times. Then, I found a spot to park it and turned it off, then turned the key to position II (not starting the engine) and let it sit like that for 30-40 seconds, then turned it off. Then, when I started the engine up, it idled notably more smoothly. And it’s stayed that way. Further checks with a code reader showed no new codes being through, though the engine light is still on – I presume it will turn off after 100 miles or so (part of the buffer it needs to have so you can’t cheat the smog check so easily).
I hope this helps.