My 2004 vRS sounds like a very noisy diesel when starting from cold. Thought the exhaust had a large hole but when the engine has warmed up ie (choke turns off) the

noise disapears.

Starting when engine hot everything sounds normal.

Anyone got any ideas what to look for please.

Thanks.

Probably the secondary air pump.

jack the front of the car up on the drivers side and unscrew the under tray behind the bumper.

You should see a big black plastic cylinder thing just in front of the sump, this is the secondary air pump and it's in two parts, held together by rivets. When the rivets come loose you get a gap between the two parts and air escapes making that odd noise. The secondary air pump only works when the car is cold, it helps the cat get up to temperature quicker. The solution to get rid of the noise is to take the pump off and replace the rivets with nuts and bolts.

Theres a guide to doing it here: http://uk-mkivs.net/forums/thread/940861.aspx

If it's not that, how long since the car was last serviced? These engines have hydraulic tappets, and engine oil usually thickens with age, which makes them sound tappetty when cold and neading a service.

Secondary air pump. Mine sounds like a bloody Class 47 diesel train

Edited 27 April, 200917 yr by Jigger72

I had some chav undesirable types say "sounds a bit rough mate" the other day when I first started my car up. I told them it was running an aggressive map and that that was the downside... my car is infact completely standard

They bought it aswell and were just walking away when the secondary pump did its normal "I've finished doing what I was doing" PIIISSSHHHHHHHH sound. They looked around and I just said "dump valve" I tried to keep a straight face when they replied "ha ha, dat's sick mate" :P