The SES light has come on the last three times I put gas in the car. The codes I get are P0171 and P0174 (Lean Bank 1 and 2). The codes clear themselves after driving for a while. How would putting gas in throw these codes?

 

Contaminated fuel is one possibility - look up the description/diagnostics at gearchatter.com for your year. Last three times at the same pump/station?

 

It was at different stations/pumps. Let me clarify when exactly it happens. I stop at a pump, SES off. I turn the car off and put in gas. I turn on the car to leave, SES on. It eventually turns off after drivng for a while.

 

I didn't want to create a new thread so I figured I'd post it in here.
I have a 2000 z28 M6, and every once in a while the idle will drop from 750 to about 300, then rise back up again. It does this when idling, or coming to a stop. I figured this is linked to the SES light, which goes on and off for a while. It was throwing P0171 & P0174 codes, and reading through previous threads and posts I figured to check the vacuum hoses and the MAF sensor first. Well, I cleaned the MAF sensor thoroughly, and reassured the hoses didn't have any kinks, slits, or were unfastened. Since then the SES light has been off completely for about a week now, although the idle still drops about as regularly as it did before. Can someone help me out?

 

still have stock TB?

 

yeah, everything stock except for slp lm exhaust

 

leads me to believe a vaccum leak (ie: intake gaskets, hoses,or possibly bad pcv). If you have not changed your fuel filter in a while maybe plugged and lacking good fuel volume and press. These are the most common factors for 02 lean codes.