Audi A6 Avant - Erratic engine revs

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Tue 13 Jul 2010 12:48
Audi A6 Avant - Erratic engine revs - John Ryan

I have an Audi A6 2.0 Tdi Avant - 2007 (57) 7 speed Multitronic gearbox.

On most days either cold or full working temperature the engine revs will stay high when approaching junctions. Eventually they die down to normal on stopping.

Also when they stay high I can experience "hunting" revs up and down with no throttle being used. Engine revs will also increase without any throttle being applied.

Car is Main Dealer serviced. Mileage is circa 107,000 miles.

Dealer cannot diagnose any fault.

Can you suggest what problem might be.

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Thu 15 Jul 2010 22:36
Audi A6 Avant - Erratic engine revs - Roly93

I would look at the throttle position sensor. All modern cars petrol or diesel have a potentiometer attachedo the throttle to tell the ECU how much throttle you require. I am theorising that if this was worn, dirty or electrically noisy, it may give this sort of syptom but not spit out an error code.

To be honest though, I would have thought the dealer would have looked at this, but who knows, they are so reliant on VaG.com maybe they havent.

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Thu 22 Jul 2010 16:23
Audi A6 Avant - Erratic engine revs - John Ryan

Thank you for this response, my thoughts are in this direction.

Car due for service in a couple of weeks. Will ask Dealer to check.

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Fri 16 Jul 2010 18:10
Audi A6 Avant - Erratic engine revs - craig-pd130

How far will the revs increase without throttle? Is it relatively small (less than 2 - 300rpm) or quite large (500rpm+)?

Could be a small air leak somewhere on the inlet side, or I'd suspect the Multitronic 'brain' is getting a bit scrambled. I believe the gearbox ECU will have some control over engine rpm to cushion gear changes and stop lurching / powertrain backlash.
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Fri 16 Jul 2010 20:01
Audi A6 Avant - Erratic engine revs - Roly93
How far will the revs increase without throttle? Is it relatively small (less than 2 - 300rpm) or quite large (500rpm+)? Could be a small air leak somewhere on the inlet side, or I'd suspect the Multitronic 'brain' is getting a bit scrambled. I believe the gearbox ECU will have some control over engine rpm to cushion gear changes and stop lurching / powertrain backlash.

Would this be true of a diesel, I would have thought this would be petrol symptom ?

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Fri 16 Jul 2010 23:26
Audi A6 Avant - Erratic engine revs - craig-pd130

an air leak would affect a petrol much more, true. The diesels tend to have more over-riding than petrols to manage the heftier torque inputs, though.

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