I have the same problem, it used to have the raw fuel smell but that went away after I replaced the plugs and the coil pack. Now it and as it did before the cabin fills with exhaust fumes when idling, fan on and does not matter if it's on recirc or not and with the windows up. I am a pretty good mechanic so I have been trying to find the problem now for almost a year, can't figure it out, but it would seem there is an exhaust leak somewhere under the hood and it is getting sucked in by the fan. I tightened the clamps on the turbo and that seemed to helped a little but I cannot sit idling for more than a couple minutes before it becomes unbearable, There is a waste gate control on the turbo and I wonder if it is leaking from the shaft? I have a 2015 Colorado and it never smells of exhaust inside the cabin, we need to get this problem solved, GM needs to do something about this, Fords were having the same problem with the police passing out at the wheel.
Last edited by diggin; 03-10-2019 at 09:47 AM.