First of all, my car is a 2000 s4, 158k miles.

So I had a check engine light come up, then it went away after sitting for a day. I ran it by a friend and he said it was probably just a false alarm and it was nothing to worry about. Three weeks later the CEL comes back on but stays on for a few days, so I take it to this friend and he hooks his scanner up, and pushes out CEL p1131.

My mechanic comes over to take a quick look before replacing the o2 sensor, and says that there's nothing wrong with the o2 sensor and hooks up his "Audi/VW Scanner" and it returns a code saying that the "Turbo/Supercharger limit blah blah blah has been exceeded" Then he pulls out an infared thermometer and checks all of my fuel injectors and says that I need to have all of my injectors flushed at $69 a pop.

Excuse my ignorance here, I'm not great at all with cars, so I ran this by two people that I know and they both called bullshit. They both said if he was able to diagnose dirty injectors, run a bottle of STP fuel injector cleaner in it, and if my CEL comes back on and pops a p1131 to replace the o2 sensor.

My mechanic also says it's a "common" problem and the injectors should be flushed every 30-40k. He also pointed to which ones are performing bad, so I asked if I should just flush those two, and he said that they should all be done at the same time.

 

P1131 is an open sensor (internal resistance too high). That means that the sensor has opened up and isn't functioning. I'm gonna venture a guess that this guy doesn't specialize in Audi...

Change the sensor.