Is it normal to sit at 1000 revs at start up?

Goran · #1 23rd October 2011, 01:55 PM

Is it normal for a S8 to sit at 1000 revs idling on a clod start up?
Is it because its warming up the cats or something?
When its warmed up after 5 minutes or more it idles at 760 as normal.
Just a question out of curiosity, car runs fine otherwise.

jayzee · #2 23rd October 2011, 02:04 PM

Yep, totally normal whilst the secondary air pump is in use.

Singh · #3 23rd October 2011, 02:08 PM

Same happened to me, started the RS 6 for the first time in a while - questioned it and was told totally normal. No vag com faults either.

Goran · #4 23rd October 2011, 07:05 PM

Thanks guys!
Its a relief to know its normal. I'm a car hypochondriac

Singh · #5 23rd October 2011, 10:34 PM

I think we all are, nothing is cheap on these beasties.

daviesbike · #6 24th October 2011, 09:24 AM

what exactly is the secondary air pump for ?

i read somewhere that some one removed there's

ps mine dose exactly the same but you tend to notice it more now the weather is getting colder

Goran · #7 24th October 2011, 11:59 AM

I heard that its for keeping emissions down whilst cats get up to temperature. Completely pointless in my opinion. I think you would need to go to someone to map out the DTCs if you remove it as I think it will cause a error if unplugged and may light up the CEL.

I forgot, you would also need to get 2 aluminium blanking plates made up so you can take out all the tubing that goes to the rear of the engine block.

tobes49 · #8 27th October 2011, 03:57 PM

The Aux air pump works with the engine ECU start up to provide an over rich mixture and late ignition timing,

This means the mixture is still burning as it leaves the engine, mix in some fresh air from the air pump and this gives a controlled burn in the exhaust which heats the cats up very fast.

This is why they sound tinny and use lots of fuel on start up.

Unless you have the over rich mixture and mapped out of the ecu, There no point in removing the air pump as this will kill the cats faster by dumping unburnt fuel into the cats

Goran · #9 30th October 2011, 08:31 AM

Thanks Tobes, good point.
Would 100 cell cats be more resistant to unburnt fuel during start up? I presume this fuel will get burnt eventually and 100 cell cats have less resistance to gas flow possibly allowing more of the unburnt fuel to flow past them into the rear of the exhaust?

Although I guess if I'm already going to someone to get the DTC mapped out may as well change the start-up fuelling map.

daviesbike · #10 16th November 2011, 09:06 PM

ok what happens if you decat the car ? do i still need the secondary air pump ? or would this be mapped out along with the over rich mixture at start up ? and lambda ?