yes, bone stock. He did check all the grounds and found zero corrosion. Battery was tested but I don’t know if it was load tested. I’ll see what happens after the carbon cleaning next week. I’m hoping that’s the issue. I’m shocked at 50k it could be that but we’ve seen caked up valves on less miles. He did say it doesn’t take a lot with these cars even being built 15 years ago they can be very finicky.Scanning back through this thread i didn’t see mention of an aftermarket tune. Is this engine bone stock?
If you are taking it to GM I would ask if they can test the harness for proper electrical levels everywhere.
If you haven’t already also load test the battery.
just guessing here but it does seem to be leaning into an electrical issue . That could be a failing ECM, down the wiring harness all the way to the connectors and fuse box. This would include checking the coils as well as the harness running to the fuel injectors. Checking the vehicles grounds (including the stereo and especially if you have an aftermarket one as I have read of wacky behavior around a poorly wired head unit)
all of the above seems unlikely however it has to be something and starting with the ECM connectors and working your way down the line seems logical.
not sure if there is a way to test the ECM itself but you can sure check the connectors for corrosion and such.
I am sure others more experienced may be able to pint you in a better direction…
thanks as well. I’m hoping this is the case. You are the one who posted the link to the endoscope you bought correct and it hooks up to a smart phone? If so, would you mind telling me which one it was? I can remember the thread I saw it in. I’d like to have one.your harness is not damaged. The CEL will turn off after a couple cycles of the key if the problem hasn't continued. it is likely that it is a coincidence and nothing more because you would not have had the CEL go out from a change you just made. carbon buildup on the valves does not mean that it wold cause a consistent problem. temperature, humidity and how you are driving the vehicle can be the kid poking the stick into the fire ant nest. easiest way to know if that is the problem is to use an endoscope so you can view the backs of the valves with out having to take a whole mess of things apart.
Another question, they are using some potent chemical. They pour a few ounces in each cylinder and let that soak a couple hours along with spraying into the the throttle body while running obviously. Oil must be changed afterwards. Should I be worried about scoring the cylinders when they start it up? This stuff will dissolve any oil on there. I thought about seeing if they can drop some oil in there before starting up but that’s not going to cost the walls very well.