Audi Repair: slight backfire/popping noise, autodata 2005, throttle plate


Question
audi a4 avant
1.8 20v petrol
1998
Not Modified
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hi greg

my audi has a slight backfire/popping noise coming from the exaust only when it decelerates, its fine when accelerating just a slight hessitation.

i connected it to the vag-com for fault codes and the only fault was the temp sensor which i replaced.

the wierd thing is that its totally ok when cold (choke on) no problem at all, no backfire no popping no hesitation??

i have got the autodata 2005 which describes in detail how to test all components and sensors which ill be doing tomorrow but as ive never done any component testing before i thought i would ask before i carry out the procedure.

any help would be very welcome.

thanks.

Answer
I have the same car, backfire/popping noise coming from the exaust may be caused by leaking diverter valve, but that's  almost all the time right after you let the gas go.
slight hessitation, may be caused by dirty throttle plate
and this will be felt more when car is at operating temp.