I have the common turbo (2009 Cobalt SS)build up of crud inside my head chambers. It throws a CEL, but that is just part of it. My turbo has sprung an oil leak as a result of the occasional back pressure from the molten crud misfire.
I need a mechanic which has expert experience taking these Ecotecs apart. and would like to find one in Arizona or Texas. I have given up on one being found in New Mexico.
Check out cobaltss.net. They are aware of the coking isues with the lnf and will help you fix it.