i think thats a breather pipe (it is on my hs4).....not too sure what it does but i hear its good to keep it on. Mechanics aren't really my strong point....thank god for the free recovery i got with my insurance
i've been towed home twice, both times were because the rubber hose that goes from the fuel tank to the copper pipe was so old and rotten that when i was on the motorway it would collapse on itself. took a while to figure that out, hence the 2nd towing. Also called them out when the it wouldnt start, i think because the coil had gone, but he didnt believe me and sprayed easy start which worked, until i got petrol later and it wouldn't start again, got it going with my wd-40 in the carb

but then it stopped about half a mile down the A1 because the black wire had come off my dizzy somehow, i was a little embarrassed that i hadnt seen such a simple thing, luckily the guy loved the car and was telling me about his old ford capri. I think he appreciated that i was another young guy driving an old car!