I have an Audi A3, 1.6 Technik, Petrol, 2011. 44,000 miles. I have had the car from new and i have not had any problems. The last few months it has developed a fault when the car intermittently won't start ( no pattern ) sometimes first thing in the morning or after a trip out in the car, get back in and it won't start. No warning sights it's going to happen or anything different on the dash. 

Sometimes just before it cuts out it loses all power and then stalls, again no warning signs on the dash. 

Only once has the emission control warning light came on. I took the car to a garage to get this checked out and the car placed onto a diagnostic device. A lot of communication messages came up but no error code. 

An auto electrician did so checks and the two sensors either side of the catalytic converter were checked and again showed no error.

when the car does cut out and try to start it again it has a faint burnt smell which is similar to rotten eggs. 

Any ideas would be appreciated, Thanks

It's unusual that no error code comes up, but does sometime happen....

EGR VALUE on my old Astra showed this symptom but not sure if you've got an EGR on your 1.6 petrol.... 

Immobile misbehaving (transponder starting to fail) could also give these symptom but you'd usually get a imobilizer error message on attempting restart... 

Poor compression could give you issues with starting up and poor running but is rarely intermittent ....

interrmittent issues with no fault code are a Bain to troubleshoot...sorry!

Assume car is well serviced, reputable garage?

A

Cheers for that. Yes car well serviced every year with good garage. The garage I have been to is also good, just want to know if anyone had similar before I start forking out on parts to rule out, thanks 

Hi Russ....welcome to the Forum

My first thoughts are the Crankshaft Position Sensor which may not give a fault code but it would give the symptoms you are describing. They normally fail when the temperature around the sensor increases (e.g. engine warm) and then as it cools down, the engine will restart with no issues until it gets hot again.

Additionally, it is worth looking at the ignition coil(s) and checking if the wiring / connectors are in good condition.

Finally, the ignition switch itself, if this fails then it could give the same symptoms.

The smell would be excessive unburnt fuel in the Cat following the restart.

Keep us informed of what you find

Cheers  Trevor