Put some good fuel cleaner in - ATS - and after a couple of weeks my check engine light came on, 401 code - have tried replacing the two sensors / valves suggested as likely culprits (mechanics out here in San Diego are booked up for weeks) - car runs much better, but still slightly rough idle at times - check engine light still on after some time. Was replacing the EGR valve with one from Standard Ignition, mine appears different from the ones on the youtube video's, removed nuts on the...

How to replace EGR valve on 1999 Mustang six?