blazej01

Today I did 200 mile trip with no problem. Later in the day my wife took the car, and all of a sudden started to shake and rpms went all over the place. So I pulled the codes out and this is what I got from the scan with VCDS. Car has 109k miles on it. I don't know when was the last time that carbon cleaning was preformed (that is what I am suspecting)

001433 - Thermostat for Mapped Engine cooling (F265)
P0599 - 001 Short to ground
000769 - Cylinder 1
P0301 - 001 Misfire detected
004874 - Cylinder disabling
P130A - 001
When I cleared the codes and took the car for a quick spin, just to check what come back I also had misfire on cylinder 2 and 6 so 3 cylinder have misfire.

000768 - Random/multiple cylinder misfire detected.

Jack88

Has the car ever had carbon cleaning done?

ScottCNelson

Symptoms don't typically start suddenly. More commonly, you'll have rough cold start/idle and codes showing up for misfires and stuck IMF flaps. A cheap borescope could help check that. Also, the thermostat code is a complete another issue.

blazej01

Not sure when was the last time that the car was decarbonized. I got it used and never asked. Just ordered new set of plugs and will go from there. Will switch coils around to see if they are good.

As for the thermostat code. I have looked around but can not find much on s8. From what I could come up with that there is some kind of a sensor that can go bad. Could not find which one.

MP4.2+6.0

Your thermostat appears to be toast. Alternately, there is a basic wiring problem w/ thermostat. It is not just a sensor; it is part of the thermostat itself. W12 has same set up, and on W12 a lot of us saw these go in the low 100K zone, which is where you are too. The MAP function is what allows the thermostat to adjust flow and thus engine coolant temp in seconds (or even farctions) instead of minutes. When ECU senses high load, the MAP element tells thermo electric portion to go full open. When just loping along it closes thermostat down some, since motors are more efficient with a higher running temp.

Meantime, a guess is you may find your engine fans in jet engine mode. What it does when it reports a cooling issue, since it is trying to protect motor from any chance of overheating. Or at least they should be running constantly, even if motor cold and A/C compressor turned of via ECON mode. That's another way to confirm it has a cooling system issue--typically either the water temp sensor, or like here the thermostat. I think car probably backs off timing too when it picks up a cooling issue, which then may get into running issues.

Net, do the thermostat. At least as soon as the plugs. Need to search for the S8 and/or dig out the manual (Bentley, alldata, etc.). IIRC it is somewhat of a hassle, though not nearly the 4.2 port problem that essentially forces a timing belt job.

blazej01

I was confused that I don’t see any plug on thermostat housing. From my research it was pointing me to the same direction to replace the thermostat but the confusion about the plug (sensor) kept me confused.

ScottCNelson

Attached.

MP4.2+6.0

Not promoting as a source, but ecs often has good pictures. Even the dealer parts guys look at them sometimes. You can see the connector plug on the cover in the pics.

https://www.ecstuning.com/b-genuine-...t/079121115bk/

blazej01

I don’t know what I would do with out you. I don’t know how I was looking but for love of god I did not see that plug. Just ordered new housing with thermostat. Now just need to find out what is going on with all the misfires.

d6lc

I hope that it works, keep us updated on what you find out as my S8 is just coming up to 100k.