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Matt, Engineer
Category: Audi
Satisfied Customers: 22005
Experience:  Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
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Audi A3: HI iam having problems with my audi A3 1.6.Theproblem

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HI iam having problems with my audi A3 1.6.Theproblem is when the car temperature reaches 90 degrees or you are sitting in traffic the car will cut out but it starts straight away then it will jump and splutter until you get going again.Ihave been out today on a long journey car run absolutely fine until i had to sit in standing traffic the temperature went up to 90 does not boil over it just cut out on me started straight away once i got going again it was fine travelled all the way home about 75miles without any problems at all.Could you please identify what could be causing this problem.I am loosing confidence in taking the car into town because of what keeps happening.Many Thanks

This could be a wiring issue as things tend to expand when hot and its possible a poor or partial electrical connection is being pushed apart on one of the major sensors so check the connection plug and wiring to the following;
Airflow meter
Crank position sensor
Cam position sensor
O2 sensor
Throttle position sensor

Also worth checking the connections to the fuel pump for the same reason - unplug each in turn and give them a good squirt of switch / contact cleaner - Not WD40

and also unplug and inspect the main power relays and fuses for signs of overheating or corroded terminals - so the ones for the ECU and the fuel pump

And also unplug the wiring loom connections in the engine bay one at time and inspect for corroded or recessed pins.
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Customer: replied 5 years ago.

Hi i forgot to mention to you thatwhen the car is ideling you can feel the throttle pedal moving up and down under foot and revs go up and down


That sounds like the car is trying to compensate for an airleak, if you have an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.
As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.
Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.