Hi Mark
Couldn't resist another evo then!
I'm pretty sure its part of the 'fuel evaporation circuit' which basically prevents petrol vapours being released to atmosphere, they are diverted through various valves to a charcoal cannister located next to the washer bottle in the boot. I had a look on my car and the loose pipe attaches underneath the valve (there are 3 pipes connected to it). Whether that would cause the injection light to come on I'm not sure.
The engine/injection light would come on in Margaret's 156 (drove perfectly), especially after a prolonged period of town driving, a full tank of V-Power combined with some Redex and then an Italian tune-up would always make it go out ! I'm having some work done on the GTtomorrow at Autocasa in Coventry. I'll ask Enzo (LMC member and evo owner) for any suggestions.
Regards Steve
BTW are you doing the Cotswold Economy Drive this weekend?