It depends on how many miles are on the clock, Both O2 sensors would only go out if you were well beyond 100k. The fact that its a lean fault code and for that many cylinders to misfire at both banks points to a bad MAF sensor or vacuum leak at the manifold before O2 sensors. Either way diagnosis has to be done. 1 hour at whatever rate. If they don't find the problem another hour will be added. If they find the problem as being a vacuum leak then the repair parts wise will be less than $20, add $300 for a MAF sensor and even worse for two O2 sensors. O2 sensors on a 4.2L S4 are hell on earth to change, like 4 hours of labor to change them both out. So if you indeed do have two bad O2 sensors you would be looking at a $700+ repair with diagnosis included.

 

these are all the codes:
p1128 mixture too lean bank 1
p1130 mixture too lean bank 2
po 171 lean bank 1
po 174 lean bank 2
po 300 misfire
po 308 misfire
po 304 misfire
po 301 misfire
po305 misfire

he checked the 02 sensors and said they looked ok
said "fuel trims" looked ok

thought maybe "vacuum leak-intake gaskets"


i asked him to drain the gas tank. did all but a little over 1/4. i filled it at a reliable station with 91 oct.
the CEL is off now. i'll wait to see if it comes back on.

he has quoted me a price of $387 for remove and replace intake manifold gasket.

 

Remind me to NEVER buy a 4.2L S4.

 

$400 might sound like alot on a TT but thats a V8, which means no room under the hood. Oh and it's actually 4 sensors, two post and two precat. At the shop have them run it on a VAG scanner to determine which set is bad. Recently had to buy two myself, couldn't find them any cheaper than HERE

 

The intake manifold gaskets are a very good possibility. I have replaced a couple myself for this exact same issue on 4.2L S4's. $387 is a screaming deal, as we used to charge around $900 for the same repair.

 

Actually, the chain driven (non FSI) 4.2L engines is one of the best and most reliable engines audi has ever made. I hardly ever worked on them at the dealer.

 

he listed parts to be 41 and labor to be 343 (estimating time to be 4 hours).

sometimes i think the mechanics to better than the doctors and lawyers!!

 

ya the intake mani is dumb to take off. it's kinda like the 2.8. you have to move fuel rails and injectors. i'd do it for you for free if i lived by you lol. and then i would test drive the crap outta your car after i finished the installation hehehe. good luck with it, don't let them tell you that you have a dirty air filter and fuel filter too.

 

well since we talked about the possibility of bad gas, he wanted to put in a new fuel filter, but didn't have one in stock.

 

Possibilities:

MAF
Intake Leak
Air Temp Sensor
Fuel Pump
Fuel Pressure Regulator
Fuel Filter
Dirty/Crap Gas glogging the Injectors