V70 emissions

[mcdjl]

My 2002 V70 petrol is randomly throwing a mixture of P0131,P0133 and P0171 fault codes. I've tried replacing the lambda sensor and the MAF which seems to leave an air leak somewhere in the system as the likely cause. Does anyone know which joints/connections are likely to be causing this issue and how i might have a chance of testing them? Its not really affecting the cars performance (well fuel economy may be down slightly its hard to tell) but i dislike the engine warning light being on and although i can turn it off it come back on at a random interval later.