very good chance you have excess oil on the MAF from your filter. Go to your local automotive place, and pick up some MAF specific spray...that should fix it, if not, you're out less than $10. It worked for me. STS light came on, car shifted rough, etc. same year model with a CAI system from K&N.
+1, be very carefully around the Mass Air Flow sensor, the oils from your fingers can dirty/damage the sensor.
Far as increasing MPG, it wont. Your cold air intake does grab air from the coolest part, but your PCM/ECU has to correct the right air/fuel mixture. So in english, it will dump more fuel to reach that 14.1 air/fuel mixture. A K&N drop in filter wouldve been a better choice for solely increasing MPG. My K&N typhoon, I lost on .5 mpg, but quickly gained it back with a cat-back exhaust.
2009 Cobalt LS XFE U74
Mods: K&N Typhoon Intake, Option Cat-Back Exhaust, Cosmo Short shifter, Maxxim Ahead 17X7's, MPx shorty antenna, FE5 Strut/shocks, Tein S Techs, Moog endlinks, Moog spring seaters, ZZP shorty header, LSJ downpipe, LNF front grille
Last edited by 5t3alth; 04-14-2013 at 08:17 AM.