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Jake, Technician
Category: Audi
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Experience:  Over 30 years experience, 17 years with Audi, Factory trained
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2001 a6: 2.7t avant is misfiring on 4-5-6 cylinders..really rough

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my 2001 a6 2.7t avant is misfiring on 4-5-6 cylinders making it idle at about 500 rpm and runs really rough when you bring the idle up it runs better but not perfect. please help

Thank You for choosing Just Answer for your query. Yes, I can help you.

Any time you wish assistance with a drivability concern it is always best to list the Diagnostic Trouble Code (DTC) number(s) as there are often several possibilities for the same condition, each specific DTC indicating it’s own specific condition. So I need to know the DTC number(s) that is stored to best further assist you.

You should have at least P0304, P0305, P0306, and P0300. Are there any others?

Did this all come about suddenly? Did anything happen right before it started?

When you say "exhaust air flow sensor", did you mean to say exhaust temperature sensor? Where did you purchase only one? They are now sold in pairs of updated sensors.

A severe misfire causes unburned fuel (hydrocarbons) to pass through the exhaust. When it reaches the catalyst it burns. This is the catalyst's function to burn any unburned hydrocarbons, but NOT the large quantity associated with a misfire. When the catalyst processes excessive amounts of hydrocarbons it becomes intensely HOT and overheats. I have seen them GLOW red and melt adjacent heat shields. This also damages the catalyst and in many cases warrants it’s replacement.

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Thank You!

Customer: replied 7 years ago.
haven't the fault codes writen down but can get them monday!
i know it cam up
misfire on cylinder 4
" " " 5
" " " 6
exhaust flow sensor fault to earth(located behind the turbo with tube which goes to a little black box at the top of the back of the engine)
Typically misfires are coils and the CEL blinks, but when you have all three cylinders on the same bank, at the same time, it is likely cam timing related.

Possibilities would be a camshaft adjuster, or perhaps a timing belt that has jumped a tooth or ... I really need those DTC #s to properly assist you. How many miles are on the vehicle and has the timing belt been replaced, and if so when (mileage).

That would be the Exhaust temperature sensor, It is a common failure and should be replaced in pairs with the updated sensors. I think any improvement in performance since replacement is either coincidental or imagined as I have never "felt" a performance improvement after replacement.

Please get back to me with those DTC #s on Monday so I can further assist you.

Thank You!
Customer: replied 7 years ago.
the cars done 97000miles and not sure when the belt was done.
there is a small tapping from that bank also.
Ionly replaced one sensor cause there £189 each from audi's
Customer: replied 7 years ago.
the codes are
p0345 camshaft position sensor circuit a bank 2
p0300 Random misfire on cylinders
p0150 02 sensor bank 2 sensor 1
p0130 02 sensor bank 1 sensor 1

there is also what sounds like a lifter tapping on bank 2

any help please
That would make more sence. I believe the P0345 would be the reason for the misfire DTCs on bank #2 (P0304, 305, 306). Both of the O2 sensor DTCs are likely the indicated O2 sensors are Auids are good about the O2 DTCs being correct

Either the camshaft adjuster has failed or there is an oil supply issue with that bank. Given the fact that you say "sounds like a lifter tapping on bank 2", I suspect the later, but without being able to inspect it first hand I can not say for sure.

I suggest you take the vehicle in to have it inspected by a qualified mechanic. At a miminmum the camshaft adjuster inlet should be inspected for restriction. In order to replace the adjuster or even check the oil supply screen (filter) the timing belt or cam shafts must be removed. This would be beyond the scope of any DIY mechanic proceedures I could recommend.

Please let me know if you would like further assistance.

Thank You!
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