I know there are threads on this but all I saw were atleast 4 years old. I just bought a 2008 Cobalt SS TC with Hahn intercooler, K&N typhoon CAI and VTA diverter valve. Car idles terribly and throws code p0326, I’m assuming because it’s got the VTA diverter. It has GMS1 TMAP sensors but po claims it’s never been tuned… rewired sensors and ordering a forge diverter valve non VTA, looking for someone that can flash the ECU to correct what’s going on. If I unplug the MAF sensor, it idles not perfectly, but a whole lot better. Thanks in advance!

 

Getting rid of the VTA should fix your issue. It’s dumping metered air into the atmosphere that should be recurced. I’d start from there. If you want to keep it you need to do a maf relocate to the cold side of the intercooler and get tuned.