Help - won't start when hot!

I have a petrol-driven manual Audi A4 1.8 Avant, and it all works well except that it won't start if I have driven for twenty mintues in the previous half hour.
If I pull out an end of this tube:
http://www.maxwellfamily.org.uk/ebay/overview.jpg
http://www.maxwellfamily.org.uk/ebay/closeup.jpg
which my French mechanic calls a brake servo decompression tube - and wait for ten minutes it starts, but then it stalls when it should idle unless I put it back. Once the engine is running everything is fine.
http://www.maxwellfamily.org.uk/ebay/open.jpg
Otherwise if I wait half an hour for it to cool down it starts again.
I replaced this tube a month ago - the old one had started to pinch, so I got the exact same part from Audi. Unfortunately that did not solve the problem.
Can anybody help?
Thanks a lot,
John
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Hi John
I can't really see clearly from the pics, but do I take it you are a Brit living in France?? (If so, nice).
Anyway, the French-to-English translation for "servo decompression tube" would obviously be the vacuum hose, which supplies the brake servo. Somewhere along the length of this hose, between the inlet manifold and the servo will be a non-return valve. See if you can check this.
However, the non-starting and poor warm idling would suggest something else. Firstly, does any of the warning lights in the dash light up? Have you got the ECU scanned with a fault code reader?
Regarding pulling off the tube and waiting for 10mins - I think this is just coincidental. Try to wait those 10mins, but without pulling off the tube, and see if it still starts. Regarding stalling with the tube off, that is simply down to the incorrect idle vacuum, and would be normal.
Your actual problem indicates fuel vapour lock when hot. Do you smell any fuel vapour when the bonnet is open. Are you able to examine the fuel lines? Have any of the underfloor rigid lines been partially crushed from hitting a rock or similar. Are any of the flexible fuel lines (particularly under the bonnet) degrading, and do they feel limp and sludgy when warm. The internal bore of the fuel hose can collapse, but not be evident on the outside.
Another issue could be the fuel pump. These are ECU controlled, to give variable pressure and delivery rates. It is not unheard of for these to fail.
Hope these are some pointers to get you started, rgds.
--


Sean
www.VAGSport.co.uk - forum dedicated to all makes & models within
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Coolant Temperature Sensor might be faulty. It might be richening up the mixture enough to flood the engine and you have been starting the engine with an additional amount of air. Spark plugs might be worn too.
--
later,
dave
(One out of many daves)
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HEY I HAD THE SAME ISSUE WITH A 95 LUMINA BUT I JUST LEFT IT BY THE SIDE OF THE ROAD AND WENT AND GOT ME A SWEET AUDI TT QUATTRO HOPE THIS HELPS

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Thanks Sean and Dave - this is really helpful information. I will get the Swiss mechanics on the right track now.
As for Gerky, cheers mate - maybe they'll swap it for a TT quattro if I throw in the furry steering wheel cover!
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