If it starts, it'll start all day long, if it doesn't it fires up for a second or two, dies and then if the battery lasts long enough I have to crank it and crank it, eventually firing on one then two then runs, it's like it starts on the fuel remaining in the high pressure pump /rail then runs out of fuel until eventually more arrives, it's been suggested the lift pump in the tank may have failed but there are no warning lights on, no codes stored and once it starts it runs fine all day, generally it'll start if it's been run in the past 24 hours or so but leave it a couple of days and it's a pig.

So far, service including fuel filter, new battery. any suggestions would be appreciated, oh and idle isn't smooth and occasionally I get the dumper truck idle when it's been run and idling for a while. other than driving me insane it's a lovely car, Audi A4 B7 2007 2.0 TDi S-Line Cabriolet

Have you scanned for error codes Martin?

Yes no obd codes at all but  it looks like I've been barking up the wrong tree, really tempted to kick it today! wouldn't start again, cranked it and cranked it, eventually it fired up like a dumper truck, idled for about 5 mins while I strapped little un in and waited for er indoors, well off we went, got to the junction at the end of the street about 100yds and it died!!!! would not restart, I pushed it back to the house, called my friendly garage and waited, I put the battery on charge while I waited then the guy turned up and hooked up his laptop, he got the car to start eventually and then told me I had one totally knackered injector and one pretty bad one, that'll explain the rough idle too then I suppose, anyway I called the local stealership and said I'm not happy about 2 injectors failing at just 91k, well the guy agreed and gave me a quote for £1500 and 14p! He also gave me head office's number and I'm currently awaiting a call back from them. I called the local parts supplier and they want £500 plus vat each for the injectors and apparently you cant touch them with your fingers, so I think it's going to have to be transported 11 miles to Audi, hopefully they'll help with the cost, Maybe I should have bought a BMW!

Don't say that, it would always have been worse with a BMW 

Sorry to hear that though that's really unlucky. How long have you owned the car?