A6 2.5 TDI excessive smoke at idle only

[nicknick]

Hi,

My 1998 A6 2.5 tdi (with 118,000 miles on) has just started doing the above. It doesn't happen at start up - but once you've driven the car and then stop and let the car idle after about a 30 - 60 seconds the smoke starts (which is white (well...it's more grey but it's not black or blue)).

If sat idling it will smoke like this until you pull away and pick up speed at which point it stops.

There is no loss of power at all. There is no oil leak appararent and no loss of water or rise in water or oil temp etc and fuel consumption is normal.

I've done some searching and two options I've seen are that it could be the EGR valve failing and not opening at idle or the crank case breather filter (located between the turbo and rear of the diesel pump).

I'm inclined to get it booked in at the dealers thinking that they'll at least be able to check for codes that the EGR might have thrown.....but I'd welcome anything that I might be able to check myself or thoughts that might avoid

a trip to the dealers and allow me to send it to the local garage.

Thanks in advance

[Edd_W]

Without a CEL it is unlikley to be anything major in terms of sensors failing. It is equally unlikely to be anything mechnical at that mileage.

I would say you are right, it is EGR related.

If it was a blocked breather, Audi's are generally fairly efficient at letting you know via oil leaking out of every seal in the engine but that is more my experinec with petrol engines not diesels, but I guess they are similar in that respect. You could check but waiting for it to do it then remove the oil filler cap to see two things, firstly what sort of pressure there is and if it stops the smoke after a short while with the cap off.

[nicknick]

I moved this to the technical forum ...and updated there with the following...

[ QUOTE ]

I range local dealers today to get it booked in - but on describing the problem they put me through to someone who I assume was a technician. He said (without me prompting) that he was pretty sure it would be a blocked crankcase breather filter and said this would explain why I didn't get the problem from cold as the build up of fumes would release gradually overnight. He said I could test by taking the oil filler cap off when the engine was hot - and if I get a hiss from the release of the pressure built up that would also help confirm it as the filter.

so - just done that - quick drive to get engine hot , then pull over and smoking starts. Popped the bonnet and release the oil filler and sure enough plenty of pressure released ...and with the cap off after 30 seconds or so the smoking stops. Cap back on and 30-60 seconds later smoking again.

So - seems to look promising that this is all it is....and if it is then top marks to Audi for the easy diagnosis.

Only problem is that he said it is about 3 hours work to replace the filter as it's awkward to get to and requires removal of diesel injector unit (I might have got that bit wrong ) so I'm tempted to get it done at an independant only I don't have or know of one in the West / North Yorkshire area.

[/ QUOTE ]

So - based on fact that it hisses and stops smoking ...what would you say ? - same as dealer ?

I've got VAG Com cable now ...so can check for fault codes...

[Edd_W]

I would say that blocked breather is almost a certanty now from your test.

Just a case of finding where the breathers are - there will probably be one from the back of each cam cover going to somewhere on the inlet tract. There will probably be a one-way valve to stop the crankcase from being pressureised in event of possitive pressure form the inlet side and my guess that is where the problem is.