This is very weird. I have an "05" Tuscan 2.7L w/ P0171/0174 Codes. I was advised by my mechanic to put in Seafoam to see if that deactivates the codes. I did, and the did ...... for a few days . Then a couple of days, then the "Check Engine" Light came back on. I've put the SEAFOAM IN full tanks 2 more times and the same thing happened. Anyone got an idea what is going on?