2004 1.8t air problem

**mark_julian** · 11-09-2009,05:55 PM

Can anyone help me. My 2004 1.8t has developed a load of issues recently. It's running very rough at idle as though it's missing. I had it on the diagnostics machine and it threw up 5 faults. I haven't got the codes to hand but 2 were misfires and 3 were all to do with air leaks (checked through ross-tech.com). All the info on ross-tech pointed to a hose problem. So far I've changed the plugs, coil packs (all original audi parts), air filter and run some fuel cleaner through the tank. I had a good listen in the engine bay today and heard a slight hissing. Not able to locate the hiss I got a long tube and with one end in my ear used it as a stephoscope and found what I think is the origin. Problem is I don't know if the part is supposed to let air in???? Does anyone know what the round black part is in the picture below? It's at the back of the engine block between the engine and the firewall. The leak's coming from the top left hand side by the seam or tab you can see in the photo, that I've highlighted with a white arrow. Please help?!?!?!?!?!

Thanks in advance,
Mark
CIMG4331.JPG
CIMG4332.jpg

**blackpool1974** · 11-09-2009,07:53 PM

This is your PCV (pressure control valve)

£25 from VW or Audi, had the problem a couple of times

Will fix your problem

One of your errors was probably, pressure drop between turbo and throttle valve

**mark_julian** · 12-09-2009,10:41 AM

Thank you very much for that. Ive ordered a part so I'll see how I get on from there. Yep, one of the faults is as you said.

Mark

**dlsavage2** · 28-10-2009,02:43 AM

Mark,
Did that valve take care of the problem? I have noticed the same noise coming from the valve on my A4 1.8T. I have replaced 3 check valves so far, two of them were obviously broken, after replacing the last one, the check engine light did not clear for over 150 miles. Cleared the codes at AutoZone, CEL came back within 20 miles while idling at a signal light. I cannot find any other leaks or broken valves like the first two, but I could hear the hissing sound coming from that valve. Is your problem resolved?

Thanks,

**blackpool1974** · 28-10-2009,02:07 PM

Can you take the oil cap off when the car is idling ??

If not will be a vacuum problem caused by the crankcase breather valve I had to change this valve, pulls like a train now !!

I think the crankcase breather valve breaks the PRV (pressure recirculating valve) what I previously called the PCV

check out this thread
https://www.vwaudiforum.co.uk/forum/s...&highlight=pcv

**dlsavage2** · 28-10-2009,07:55 PM

Blackpool,
Thanks for your response, I think that the problem was with the Black pressure regulating valve, when I inspected the one that I removed, I discovered a crack running across the bottom of the valve. There was oil seeping out on to the lip of the hose which attaches to the bottom of the valve. I suspect that the crack was leaking oil out. I am now waiting to see if the CEL will reset. The car idles better and shifts smoother. This is the third broken plastic part that I have found since the dealer replaced the cam adjuster which was leaking oil. Thanks again for your response

**mark_julian** · 28-10-2009,09:43 PM

Hi Dlsavage,

Replacing the PRV did cure my problem. There was no obvious sign that it was broken but it was letting a lot of air out. A 5 minute fix and it runs as smooth as silk now. I haven't had chance to get the engine warning light cleared yet but I'm gonna do that next week and hopefully it will stay off. Good luck!

Mark

**dlsavage2** · 29-10-2009,02:53 AM

Here is a picture of the cracked control valve that I removed today.

**mark_julian** · 29-10-2009,10:28 AM

That's definitely a crack!

**mark_julian** · 19-11-2009,12:50 PM

Hi Dlsavage & Blackpool,

I've still got a problem with the A4! I replaced the PRV and the car was running much smother. However, the engine light comes back on after about 50 miles and I can feel the odd rough pulse at idle. I just tried taking the oil cap off at idle and it won't come off.

Also, the hissing from the new PRV is much worse than it was before and if I put my finger on the point where it's hissing to stop the leak, the engine skips a beat and runs rougher.

The fault codet hat comes up now is 17544 (P1136) long term fuel trim (add.) system too lean.

Any ideas. How's yours now blackpool with the new crankcase breather valve?

Mark