mk1 VRS running lumpy at cold.. for 60 seconds!

[capnahab]

Hi. Bit of a wierd one this.

When I start the car in the mornings (cold) it sounds like there's a hole in the downpipe / airbox and it runs quite lumpy....for 60 seconds then magically corrects itself! After that time I get full power, no missing, no blowing noise anymore... really wierd. If I restart the car when its warm there's no problem, so its only when cold. Its really odd though that there's this wooshing air escaping noise... then 60 seconds later it stops and everything is OK.

Any ideas??

[David 8]

It's the secondry air pump, which pumps air in when the car is cold which helps keep emissions down on cold start. It's perfectly normal don't worry about it. You could use the search function if you want to know more.

Sometimes the running can be affected whilst it's pumping, if yours does this just wait until it stops before driving off.

HTH

[k04]

I got my vrs back in september and wondered if this noiise was normal,but over the coming months i noticed the noise to be getting louder and louder

I was curious about this so dropped the car into my local skoda dealer and he said that the noise is normal but mine was getting louder because when they build the car its just rivited on the side of the engine and in time it gradually prizes off hence why it was really noisey

Luckily the car was under warranty still and they changed it for a new one

If your cars under warranty still and your worried that its getting a bit too loud get it changed coz i bet their not cheap

Hope this helps:)

[Fezboy]

Its really odd though that there's this wooshing air escaping noise... then 60 seconds later it stops and everything is OK.

Your lucky mine stays on for 2-3 minutes :thumbdwn:

Sound like a hoover

[Land_Raver]

It sounds to me like your have an air leak somewhwere in your Secondary Air Pump system. Common points that go are the quick release nylon hoses become brittle with age and come loose & also the rivets on theair pump housing corrode & fall out causing the pump to separate & leak.

If you need to look up how to cure the pump leak if it is that then do a search for secondary air pump & you will see some of my threads on this. Good Luck

[Clarey]

I followed the guide on uk-mkivs on how to replace the rivets with nuts and bolts, works a treat.

[chris2470]

Mine does exactly the same, first 60 secs it runs very badly almost like its missing then all of a sudden it's perfect.

I have seen this problem posted many times without a definitive answer so I assume it's quite normal and something that effects most.

It's still very annoying first thing in the morning.

[capnahab]

Sorry for the late reply, thanks alot guys, will check that out.

Cheers!

[cardiffblue]

I had the same problem on mine and would not be able to pull off until the engine was running correctly. checked the system/engine could not find any faults or pipes adrift, checked the throttle body and egr both clogged up slightly, cleaned both units up and since then no problems will have to wait till the winter to check if its has fixed the fault 100%

Edited 25 July, 2008 by cardiffblue

[Bodge]

Something interesting that I learnt today...

As we all know, the mk1 vRS has VVT. But the valve timing is only varied on cold start, purely for emissions. There are 2 timing settings, one being 'normal', the other being 'massive overlap' (for cold start). The overlap is used to draw exhaust gasses back into the cylinders at cold startup.

I never knew that! I assumed the VVT changed the valve timing at certain revs, like a VTEC type system.

This 'massive overlap' would explain the lumpy running of the engine on cold start. But why would it get worse? Could an ineffective or weak secondary air pump, combined with this valve overlap, cause the roughness? Does the active VVT rely on a strong air supply from the pump to keep things running smooth while running the overlap?

I guess the way to test this would be for someone with a new/very healthy air pump to disconnect it and compare cold start behaviour from when it is connected.

I wonder if you can de-activate the VVT?