could be the maf (air flow sensor) theses fail often.
easiest ways to check are using vag com or swap with someone elses (must be exactly same part number).
if its this it will be about £80 exchange from dealer
i had this problem, just turned out to be the t/c button itself.
plugging it into diagnostics will tell you
otherwise you're guessing
get it checked by someone with the right equipment
all dash lights will show a FC
like I said then.... the right equipment
RAC & AA tools are gash & rarely work (properly) on SEAT's
Vagcom or 1551/2 machine is what's needed