Preamble: 2013 Q5 at 149k miles now, purchased bone stock in 2020 at 95k miles. Mods: 034M stage 2 (91 octane) with 187mm crank pulley, IE intake and Merc HX. Stock exhaust and cats. Typical service history under my ownership including PCV (latest rev VAG-06E103547AH) coolant pump/thermostat, plugs/coilpacks, all fluids and filters, belts, etc. Carbon clean intake valves at about 125k miles. Failed a serp belt tensioner around 135k miles (January of 2023) so I pulled the crank pulley and inspected the front crank seal which looked fine. One month later I noticed a "greyish" smoke exiting the rear mufflers on startup, not white not blue. Life got in the way and I did not determine or fix the cause of the smoke on startup, it does not always smoke on startup nor after running at normal operating temps - cold starts after a few days sitting make the most smoke. A few weeks ago the motor began misfiring badly. I pulled the plugs and found them totally fouled with wet carbon. After replacing the misfires did not change at all so I said F#$@ It! and began pulling the motor. The pics show what I found and it does not look good to me...
So I need advice on what next steps to take. I have on hand new head gaskets/bolts as well as a complete VAG timing service kit. I plan to find a shop that can flush/test the fuel injectors or I will replace them if necessary. I have a reasonable cost source for new piston rings and valves if needed. I intend to do as much of the labor as possible. Other than decarbonizing and reassembling the motor what else needs to be done? Is there any way to prevent or reduce the carbon returning? What about oil on the injectors/plugs? I want to keep this Q and make it reliable again!
heads_valves.jpg
bore score.jpg
injectors.jpg
valves.jpg
added pics of the valves removed from the head to show the condition before cleaning
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