This has bugged me for quite some time. S3 4.2, Euro Spec. Occasionally cabin is filled with petrol smell. Usually during hilly driving. Seems to correlate to heavier throttle and ambient temperature as well, but not positively. I would stop the car and inspect when it happens, but could not detect anything from the dual fuel filler caps, inside the boot, quarter wheel arches, or the engine compartment. Around the injector I could not see visible seepage or smell anything. It's just in the cabin. Help...

 

One thought is that the smell is coming from the vapor condensers located inside the cabin in the C-pillars. Item #1 in the illustration below

https://parts.jaguarlandroverclassic.../brand/jaguar/

But, odors can travel in mysterious ways. Once, years ago, I smelled fuel in the cabin and (long story short) it turned out to be a small leak at the small fuel hose at the very front of the cylinder head

Cheers
DD

 

there are fuel vapor canisters on each C post.

one way to find out if those canisters are leaking vapor is to seat someone in each corner of the back seat to check if the fuel odor comes from there when you are driving.

another possible source is the charcoal canister if european cars have one. In american cars it is located under the right side wing towards the front under the headlamp bucket.