2nd Gen 4Cyl Oil on Plug and Multiple Codes Troubleshooting

Background/info:
- '07 2.7L stick, about 200k miles
- I recently had to have my cats replaced, they were completely rusted out - I don't think this is related but adding it in case. I drove it for quite a while like that, it was basically an open pipe by the end.
- I've got the following codes: P0300, P0304, P0441, P0455, P0500
- It's a little slow to start, cranks a bit longer than you'd want
- On first start it idles rough for the first ~15 seconds until the fast idle settles down and then seems ok
- Sometimes bogs down on acceleration
- I pulled the plugs and #4 (closest to the firewall) was completely saturated in wet oil, not reside or traces but rather a lot of oil. I'm assuming that's my P0304 (and maybe the 0300).
- About a year ago I had the valve cover gasket done, I assume they did the plug seals at that time
- I'm not losing oil, or if I am it's a small enough amount that it's not noticeable between changes. I did have to add some coolant this winter, not much and I haven't seen any traces of it in the oil or elsewhere.
- The truck is pretty beat. I've been using this as a work truck hauling material and generally making it work for its money and it shows. I don't want to put much more into it until I know what's wrong, i.e. I don't' want to start swapping out parts in hopes that it clears the problems.

First the oil on the plug. I'd think the plug seals but given how recently the vc gasket was done I'm hesitant to just pull it and do it again. It's possible that they skipped it, or it was a bad install etc. but before I go ahead and redo it what can I check/troubleshoot to narrow this down?

 

P0300 and P0304 - Was the oil on the plug on the insulator/base of the plug or on the electrode. If the oil was on the electrode that means you have oil in the combustion chamber, either blow-by from piston rings or cylinder wear, or valve seals. If the oil is on the insulator/base then its probably the spark plug tube seals.

P0441 and p0445 - Emissions related, will cause a check engine light but won't affect driveablity unless there is large vacuum leak.

P0500 - Vehicle speed sensor, could be related to the misfire, maybe. Are your speedometer working and cruise control working? If they are working I would address the misfire first, and see if the code clears when misfire is corrected.

 

Just for funsies, pull the plugs, pressurize the cooling system with a tester and run a borescope into each cylinder looking everywhere in there.

Otherwise I would follow the code and investigate your purge valve. I believe the code definition is for a shorted circuit. If you're lucky you may be able to just ohm out the valve and see that it's shorted. If it is then start there with your troubleshooting

 

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