# Found my vacuum leak!



## Nem (Feb 14, 2005)

Well after a good two months or so I've finally found the problem I was having causing the engine management light to come on.

I was getting a "fuel trim bank 1 (add) system too lean" code which would keep coming back after clearing after a couple of days or so. I'd already gone through fixing a massive split in the FMIC, replaced the in tank fuel pump, fitted a new MAF, and checked all of the vacuum pipes under the inlet manifold and basically found nothing. It's also been pumped up and leak tested and nothing was hissing anywhere.

After doing a lot more reading on the error and fuel trims I ended up looking at block 32 in vcds where the first value is the additive fuel percentage at idle. On clearing the error code this value is reset to 0.0% and then engine then learns a new value from there. Mine was going up to about 6.6%, the 'normal' specification is +/-9%. A perfect engine would be 0.0% but is very rare that any engine is working that well, and usually if the values are at 0.0% it's more likely a dead lambda probe.

With no more options left and the fact I had a good second hand front lambda probe sat here I decided to replace the sensor yesterday just in case it was the probe at fault. Easier said than done but was in the end replaced. First time I'd not tightened it in enough and could see bubbles of copper grease coming out from around the sensor port, so after doing it all again basically and getting it properly seated I tested the adaption value again and it was no different.

What I could hear though was a very loud hissing noise, I thought the sensor was again not in properly and was leaking air but it wasn't, no bubbles around the port. After a while of moving different pipes and digging around I finally found the problem I'd been looking for all along:










It is off of the brake servo pipe and hidden down behind the alloy heat shield right at the back of the engine bay:










It's also covered behind the lambda probe electrical connector and head shield:










It was sucking air in at an alarming rate. You could even hear the difference in engine note with my finger over the split. With some electrical tape wound around it I checked the idle lambda adjustment again and within 1 minute it had gone down from 6.6% to 2.1% and a while after 0.4%! I don't think that for a 12 year old engine with 158000 miles on the clock that being 0.4% away from 'perfect' is that bad 

So a new pipe is on order for today and this afternoon I'll do it all again, god knows where the bottom of the pipe goes to though


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## jamman (May 6, 2002)

Glad you found it.

If its the one I think It is I think you might end up doing a repair on it as I think the pipe
is a PITA to replace.


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## JorgeTTCQ (May 7, 2002)

That's great!
Your _TT_ is again 100% powerful.

Best regards,


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## Charlesuk (Mar 12, 2012)

good find!


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## Stealth69 (Jun 25, 2012)

Awesome work and patience buddy, glad problem has been found!


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## Duggy (May 17, 2005)

Glad you found it Nick, they are so annoying and always turn into a money pit!

John

Sent from my iPhone using Tapatalk


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## Nem (Feb 14, 2005)

All done now:










8)

Even managed to reuse the oem clip too!

Where the pop-studded heatshield is on the new one covering the one way valve, mine had slipped down and the valve and pressed fittings were fully exposed to the heat.

Anyway, all sorted out and very happy!


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