I think a check engine light will turn off dod/afm. I can't remember what people typically unplug to get the dod/afm to turn off. When I bought my GXP, I would see poof's of smoke in my rear view mirror from time to time. I turned off the dod/afm and it stopped. at like 120,000 miles I got low oil pressure, ended up being the pickup tube o ring in the oil pan. I also have a lifter fail which necessitated a new cam and lifter set. that happened like 30,000 miles after dod/afm was turned off.
my gas mileage pretty much never changed the whole time.
