hi 

 Ive  2010 audi a3 , usually runs well and has been recently serviced .

 For the last 5 months ive had an ongoing problem with restarting the engine -  engine starts from cold ok - but after running  and after  I switch off it  does occasionally take several attempts to  start again 

 Engine could be running 5 mins or 2 hours - switch off and try to restart a few minutes or a couple of hours later  and wont - no pattern whatsover - instances are becoming more frequent .  The engine turns ok but no firing takes place - I have to leave the engine for 5- 10 minutes between attempts other wise it floods 

 After a few attempts engine starts immediately - like throwing a switch . no coaxing or spluttering involved . 

 Does anyone have any suggestions as to what can be wrong?

Petrol or diesel?

7 hours ago, cliffcoggin said:

Petrol or diesel?

Well asked, it will make a difference to any diagnosis so would plugging it in for fault codes.

Steve.

its petrol 1600cc .   the problem occurs intermittently - could be running for days or weeks without any issue  - problem started May this year  very occasionally - a handful of times really -  but the incidence is  becoming more frequent  over the last couple of weeks

In summary: cold starting is fine, hot starting is erratic, and the engine runs well once started. If that is correct I suggest there is an electrical or mechanical problem, though that doesn't narrow the field down much. ECM, mass flow sensor, crankshaft sensor, exhaust sensor, fuel injector, and many more could be at fault. I doubt we shall arrive at a firm diagnosis from discussion on this forum, and guessing at answers will be expensive for you, so I suggest you get it tested at an Audi dealer or independant Audi specialist. Do not use on an OBD reader from Ebay or the like, they are unreliable.