High Revs and Loud Engine

[mbenz76]

I have mentioned this is another thread but thought ot deserved it's own.

The car idles at about 550rpm. However evey now and then (maybe once a week) it idles at 900rpm for a while. While it is high the car sounds like a V12 petrol to drive - very throaty sounding.

Sometimes I start the car and it's like that, but other times it starts mid journey.

Some people mentioned it might be the car regenerating the diesel filter. However I have never had the warning light on. Although most of my driving is city centre rush hour, it did it today and it was only a week ago I thrashed it 200 miles on the motorway at 70. Can the filter really be in need of regeneration after only 50 city miles?

Also, sometimes when I start the car on a cold morning the revs will start idling at 900 until the engine temperature hits it's usual 80ish runnning temperature. Probably unrelated but worth a mention.

 

[st4]

Its the filter being regenerated, the DPF light wont, IIRC, come on.

 

[mbenz76]

Regeneration so soon after a good run though?

Could have sworn I read that the light comes on if it's needed. Although maybe that is only if it can't do it with high revs?

 

[mbenz76]

Revs back to normal now.

Out of interest, I found a smooth, straight and quiet back road and turned the radio off to have a listen. Car sounds very smooth when not doing the high rev thing. What I did notice though was a noise from the engine under hard acceleration (pulling from standstill to 40 quickly) that sounded like a flapping air noise (like if a piece of paper was flapping in the wind). I assume this is the air intake/turbo?

I hate noises in cars I can't identify! They drive me up the wall.