Intermittent high idle

[gtitdi]

I've noticed lately that sometimes the idle speed is higher than it should be - just over 1000rpm, instead of the usual 800-900.

I initially though it might have been the choke (or equiv.) but it happened yesterday when the engine was fully warm, so it can't be that.

When it happens if I turn the engine off and back on again it reverts to the normal idle speed.

The car is a 54 plate A3 Sportback 2.0TDI 140PS BKD.

Any ideas what might be the problem?

Cheers

[mjhayes73]

I have this same problem on my 56 plate 140bhp TDI passat. Just wondered if you ever found a cure.

[gtitdi]

Yeah, just the other week I was reading the self-study guide here [pg30]:

http://www.vaglinks.com/Docs/VW/Misc...SSP_873403.pdf

And it appears it's not a fault, but a feature! The central electronics unit asks for more revs so that the alternator supplies more volts when the battery voltage dips due to high load. Makes sense as it mainly happens for me in the summer when the aircon etc is running, and at night when the headlights are on. Is that the same for you?

[alankru]

Yeah, just the other week I was reading the self-study guide here [pg30]:

http://www.vaglinks.com/Docs/VW/Misc...SSP_873403.pdf

And it appears it's not a fault, but a feature! The central electronics unit asks for more revs so that the alternator supplies more volts when the battery voltage dips due to high load. Makes sense as it mainly happens for me in the summer when the aircon etc is running, and at night when the headlights are on. Is that the same for you?

Ah, I've been noticing the exact same symptoms over winter. I thought the same, that it was the cold, but I noticed that the revs returned to normal after a few minutes, which seemed to coincide with the fans speeding up to push hot air into the cabin. That would probably make sense if the heater was drawing load.

Thanks for that, that's been bugging me too!

[mjhayes73]

Yeah, just the other week I was reading the self-study guide here [pg30]:

http://www.vaglinks.com/Docs/VW/Misc...SSP_873403.pdf

And it appears it's not a fault, but a feature! The central electronics unit asks for more revs so that the alternator supplies more volts when the battery voltage dips due to high load. Makes sense as it mainly happens for me in the summer when the aircon etc is running, and at night when the headlights are on. Is that the same for you?

I have had the car for 15 months and have never noticed this before (and I notice all noises and worries!!!!), so felt this wouldn't be the case, however I then read the link and feel that this could be applicable if the battery is on its last legs.

I am going to switch off autolights/wipers to see if this makes a difference.

Thanks for your help

[Simba2004]

Hi lads, I have the same issue. I have a car for nearly 2 months now and last month I noticed the idle is around 1050 RPMs as opposed to the usual 800. I noticed it gets worse in cold, damp weather. I always drive with lights on and most of the time the heater is on too, to prevent the windows fogging up. I was worried as when she does that first thing in the morning when she's cold, that's grand, but when she was nearly 90degC, that was bothering me.

So now, is this 100% normal or does that mean the battery is on its way out, like mjhayes73 said? The car is still under warranty from the garage so if it is any fault, I better look at it immediately!

I constantly have a trouble with the battery... I had 2 cars so far and changed batter 5 times!

[alankru]

No, it doesn't equal that the battery is on its way out. My old A3 did it particularly in the winter and that battery tested fine and lasted years. Same with my brothers Fabia.
My new A3 has a very new Varta (~1 year old now) silver battery which has more capacity than the car requires. My car will rev a bit more when I've just been moving it in the drive a few times and not driving it anywhere. So, perhaps you are doing short runs and it isn't charging sufficiently?


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[Simba2004]

Hey you might be on to something! I know for a fact she doesn't like the runs around the city because they're too short for her! She does great after 3.5 hrs drive I do every Friday and Sunday.
It must not be charging 100% during the city drives then, solution!

[rowdy-999]

The battery is only used to start the engine. It isn't even in use when the engine is running. My work Skoda scouts used to have this trait of occasional higher revs.
Don't worry about it. When the engine fans are on you can also get a small increase in engine speed.

[EssexGonzo]

Could it be a forced DPF regeneration/clearout?