2011 Terrain Engine Misfiring
I have a 2011 Terrain SLE/AWD, about ~140,000 miles, not too many problems (after a new engine in 2014), with some recent heating/cooling issues.
We just took a trip from MA to TX (about 2200 miles), and the check engine light came on (code P0300) while going uphill on cruise control on the way down. We also had some ABS/Stabilitrak codes (U0101 & U0100). I decided to get it checked out at the local dealer before the trip back, and they said it was due to incorrectly gapped spark plugs (29 mils vs. 35 mils, changed back in the 110,000 mile mark) and some bad coils. We had the spark plugs, wires, and coils replaced, in addition to a fuel injection cleaning, replacement of a stabilitrak sensor (based on the ABS code) and a recommended brake fluid and coolant flush. We left about a week later, and got the exact same codes, again about halfway through the drive under similar conditions. I called the shop to see why that would be, and was told they did the work right and my mistake was in not telling them take apart the engine to dig deeper into the problem (?).
But either way, I'm not sure what the problem is, aside from maybe I shouldn't drive cruise control uphill. I do plan on taking it to my regular shop, but does anyone have any idea what it could be or what I should ask them to look for? Do they indeed need to take apart the engine, or maybe this was just the shop trying to save face? I have had some recent issues with the my regular shop (missed an obvious broken blade on the blender motor), and I'm wondering if this was something they should have caught when I took the car in before the trip to make sure it was in proper condition? Or maybe this is something that just happens over time and I should get used to it owning a car with 140,000+ miles?