ok i did a custom exhaust on my 2005 cobalt ss/sc did a 2.5 resonator and a 2.5 muffler and after a month and a bit of driving it, i got a CEL @ the track...well about 2 months to be exact...then all of a sudden it goes away, comes back, goes away, comes back etc...sometimes it'll stay for a week where other times it stays for a day and vice versa when it doesn't come on...i hooked up my car to my friends hptuners and it got me a p0170 code...which apparently its a lean code but took the car back and got the exhaust checked and they said its fine but the cel stayed on...now i ripped it a lil tonight on the way home and it came back on after a few days of it being off...what else could it be? or what can i do...pls any info or help would be appreciated..