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Have noticed recently that the engine idle speed seems to be varying from day to day.When starting from cold(garaged) tick over is just over 600rpm,after 2-3 mins driving it goes to 700ish,sometimes when fully warmed up (20-30 miles) it races at just over 900rpm!!
It makes no difference if lights or A/C is on or off,I was ready to take to the local dealer,next day every thing seemed normal 6-700rpm at all times.
I thought it might be related to outside air temp,but a few nights ago it was very cold 1C,idled perfectly at just over 600rpm.
What could be going on? faulty sensor?
What have other A5 3.0 TDI owners noticed?
 

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Idle regulation is governed by meny things and the idle will be altered for meny reasons ie load management/alternator demand,egr demand particulate filter.As there are no mil lights on i would suggest this is normal.
 

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I'd agree - I've noticed this on several cars, not specifically Audis. As a8 tech points out, the engine management regulates idle speed based on several factors - many of which may not be immediately obvious to you when you're sat in the driver's seat.

As long as the engine beat is smooth/rythmic at idle (i.e. not coughing and spluttering) I wouldn't worry about it :)

Cheers,
Paul.
 

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Have noticed recently that the engine idle speed seems to be varying from day to day.When starting from cold(garaged) tick over is just over 600rpm,after 2-3 mins driving it goes to 700ish,sometimes when fully warmed up (20-30 miles) it races at just over 900rpm!!
It makes no difference if lights or A/C is on or off,I was ready to take to the local dealer,next day every thing seemed normal 6-700rpm at all times.
I thought it might be related to outside air temp,but a few nights ago it was very cold 1C,idled perfectly at just over 600rpm.
What could be going on? faulty sensor?
What have other A5 3.0 TDI owners noticed?
Yes, I have the same car as you and what you describe is the same as my car. Only really started since the weather has got colder but seems a bit random to me!!
 

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Thanks for replies, i will say that it didn't do this last year - if starting from cold would idle at around 900rpm then within a minute would drop to 600rpm idle - this was normal and consistent.

I have ran the car with minimal load on i.e lights off, fans, stereo off etc but still happens, its weird as there is no consistency to it. At the moment mostly it is as i have described but occasionally say i have driven down the motorway and pull off onto slip road as slowing with clutch in rev drop to 800 and then when stop to 600 again normal but it doesn't last. Also sometimes if i am in traffic i have tried turning off an restarting and rev idles at normal 600 but after again unpredictably how long it lasts.
When it is running as i think normal i.e idel 600rpm sometimes when i dip the clutch the rev rise (anti stall i have heard) but sometimes not again not consistent ?- no movement of revs when high idle.

Because intermittent i am ruling out leaking vacuum hoses etc - any thoughts please welcome

thanks in advance
 

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Hi, over the last few weeks i have noticed a pattern - when the outside temperature reads above 10.5 degrees then in starts from cold revs at around 900 idle then drops to 600 as it always has. when its 10.5 or below temp outside then it idles at 900 all day long. what controls this as runs lumpy then - is there a sensor i need to swap?

thanks again for reading
 

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Wow a 12 year old thread! :)
What is the engine temp on? My old 3.0tdi used to start when cold and idle at 900rpm, then drop to about 800, then when warmed up a bit, drop to 600rpm.

I know some manual cars do have the anti-stall clutch switch, which, when you raise the clutch pedal to take up drive, the ECU raises the revs slightly. I don't know if yours has this. I had an auto 3.0TDi.
 
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