Yesterday the frequency greatly increased and the MIL turned on indicating a misfire on cylinder 4. This thread will be dedicated to my search for the source of the misfire/lurching.
Origin: Started shortly after changing fuel filter, rinsing off engine (very lightly with a garden hose), air filter, cleaning throttle body, and spraying seafoam through the throttle body with the rpms held constant at 2000 and running seafoam through a tank of gas earlier this month. An oil change was performed this same day. I had been getting a P0420 every now and then and wanted to give the requisite parts a good cleaning.
Relevant vehicle info: 194,000 miles
spark plugs with NGK iridium 145,000mi
battery replaced 2020
alternator replaced with DB electrical 2021
radiator and OEM thermostat 2020
grounds cleaned 2021 (reading 0.00ohm from battery negative post to alternator case)
passenger side valve cover gasket 2019
PCV valve 2018 (checked 2023 and still rattles), PCV hoses 2023
fuel pump O-ring 2018
ignition coil #5 June 2023
Done so far: 2 tanks of premium fuel (Always run 91), a bottle of techron, switched coil packs from cylinder 2 and 4. Misfire decreased, but MIL has not turned back on so I am waiting to see if the misfire moves to cyl. 2, in which case the plug would be the fault.
Anything else I should do while waiting for the check engine light to come back on?
I have a scan tool that can log graphs if that is helpful.
