I have a 2019 NBS 5.3 with 20,700 miles. Yesterday I took it out after it’s sat on a trickle charger inside a garage since October. I got a shudder at slight acceleration and a check engine light flashed. Turned it off, noticed reduced power and the shudder/engine light came on again. Checked under the hood and found a mouse nest under the engine cover. Towed to dealer. Dealer called that evening and said it had a code for a single cylinder misfire, they moved the spark plug and then got a misfire on that cylinder, so said the plug need replaced. They said no wires were chewed, so the mouse didn’t cause it. Also said the oil cooler line had a leak that would be a warranty repair. I agreed to replace the plug since I was already on the hook for shop time since it’s not under the power train warranty. Dealer calls this afternoon and said another cylinder is misfiring and they moved that plug and the misfire followed and now they’re pushing for a $699 “tune up” to replace plugs and wires. I told them no. Plugs, wires, brakes, rotors, oil and filters are within my capabilities and work I’ve done in the past, it’s $100 for me to cuss and scream for an hour in my garage and do it myself. What I’ve never done in the past is replace plugs at 20k miles, nor have I had a plug fail and 12hrs later have another one fail. I told the dealer I’m concerned something else is wrong and they’re just replacing plugs.
Any ideas on something else that might legit be wrong, or are they just trying for a $699 spark plug job?