From a General Motors service bulletin, this TSB is in regards to P0300 along with a cold-start misfire or rough idle, which affects vehicles that primarily have the 3.0- or 3.6-liter engine, as old as 2009 and up through 2018, and also a 2.8 liter thrown in the mix.
Upon inspection, the technician will find medium to high misfire counts and the symptom always occurs on one or two cylinders and goes away when the engine warms up. Now, a misfire or rough idle isn’t that uncommon in the grand scheme of things, but in this case it’s what’s causing them that’s unusual.
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