Fast idle in the cold weather - is it just me?

[GainfulShrimp]

My car usually idles at ~750revs but often recently it's been idling at ~950revs.

I've noticed this very occasionally when stopped at traffic lights before and put it down to a first stage regen, as it prevented the auto-stop/start kicking in and usually only lasted part of a journey - the next time I stopped at lights, it would be idling normally.

Over the last week or two though - during this freezing weather - the car has been idling at ~950revs quite a lot.
In case it's relevant, it's also been taking an awful long time for the engine to reach temperature. This morning, for instance, it was -3°C on my commute and it took about 25 minutes and 15-20 miles for the temperature gauge to reach 90°.

I don't think this recent fast-idling is regen because I can still use auto start-stop (providing there's nothing else preventing it, like using the aircon or demister etc).

My only theory is that perhaps the car is idling faster due to the cold?

Has anyone else noticed their cars idling faster than usual in the recent cold weather? I have an Ecomotive 1.6CR (with DPF) by the way.

It's booked in for its first service in a couple of weeks, so I'll mention it to the dealer when I drop it off but I'd still be interested in any theories.

 

[dannychapman10]

Started my CR FR today to move it out of the snow, it was idling at 1k the whole time I was moving the car around, so I think it's normal mate, my old PD FR was MUCH worse for it though

Danny.

 

[Leigh15]

Both of mine do this - it's something to do with the climate control I think.

I seem to remember I could get mine to jump in/out of fast idle by turning the climate on/off

 

[MrTA]

I'm no expert but do remember my old car used to idle higher when the aircon kicked in, or if you turned the heat to full blast.

It might also be to get the engine heated up quicker to improve the emissions/fuel economy? (it is an ecomotive)... someone please correct me if this is completely wrong.

 

[dannychapman10]

I would assume kicking in the compressor for the A/C would make the idle raise anyway, well it did last summer for me, but yeah, I suspect its needed especially for dervs as the oil is thick as sh*t in the cold

Danny.

 

[LeonFRDave]

My FR TDI does the same thing in this weather until its fully up to temp. I assumed it was working kind of like a choke - keeping the revs up to avoid stalling?

 

[Nath.]

On the PD FR if it ticks over at 1000rpm it's doing a DPF regen. Maybe it's the same on the CR? They may be cleaner but they will still do a regen when the DPF gets to 45%.

 

[Leigh15]

My A3's don't have DPF and do the fast idle thing - I'm pretty sure it's related to climate control fan speed

 

[spenny2004]

it will simply be the a/c unit and the fact it is so cold

 

[Leigh15]

It won't be the A/C - A/C is automatically shut down when it's frosty (5 degrees or below)

As I said earlier - I managed to control it once before whilst fiddling - I'm sure it was related to how fast the fans were running

 

[GainfulShrimp]

Thanks for all the comments. I noticed this morning that turning the dial to >=21° (with climate on Auto with no air-con) caused the fast idling. If I reverted the dial to 19°, the next time I came to a stop the car would idle at ~750rpm as usual. I've not noticed this in warmer weather so it must be related to the large delta between outside and target temperature.

 

[stuartsjg]

As Leigh15 says, the AC compressor doesn't run under 5C so it wont be that. Could be for electrical supply, the very cold starts with all the other electrical loads puts a huge stress on the battery.

Remember too that in the TDI engines the glow plugs stay on for several minutes which could double the power demand already there due to blowers, heated windows/seats, lights and the likes.

Its normal for alternators to only be able to supply full power at higher RPM (just like the AC compressor). Perhaps the ECU raises the RPM to provide more power to maintain the system voltage.

I read somewhere the glow plugs run for 0-300sec after engine start. I have noticed the rpm's stay high for a few mins after starting, then fall to normal - this is why i wonder if its linked.

Stuart

 

[Nath.]

I thought the glow plugs were pre heat only, I had no idea that they stay on after the warning light has gone out.

 

[Danny-]

Sorry to bring up an old thread but this solved my problem. I can only assume the car idles higher when climate control is on to try get the car warmer quicker?

 

[MJ]

You'll find the CR engines fluctuate quite regularly, there's a TSB on it which describes the different speeds and wether they are normal or not.

 

[cupra_ahhh]

My FL Cupra does this too, isn't it normal in cold conditions?

I've never thought of it being a problem, or different in a potential negative way. Come to think of it, i think all my previous cars idled at a higher rev when it's cold.

 

[Danny-]

Tsb? Sorry to be dumb. Lol


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[MJ]

Technical Service Bulletin.

Basically anything from 750-1200rpm is justified.

 

[Danny-]

Ahhh right. I wasn't too worried. But was curious to why it done it.


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[MJ]

Various reasons really, DPF regen, alternator load etc