i will do a checklist for people at some point but off the top of my head.. and in this order..
fault code check/clear
quick test drive
check fault codes again and investigate issues flagged up (may involve another test drive/data logging)
then if that all works out..
engine cover off, check all parts are connected as they should be
test the dv for leaks
check all hoses for splits where possible (particularly around the breathers and vac pipes) and the 'tell-tale' oily buildup at connections which indicates blowing under load - tighten up or replace clips if needed
get under the car and check the pipework to the intercooler and the joins on the pancake pipe.. if its done at the workshop we send it up in the air on the ramps and check pretty much everything from exhaust to bushes and offer advice where needed
then if all seems good the map can be flashed to the ecu after taking a backup of the original file incase it's needed.
then another test drive/fault check procedure... it's usually at that point the DV gets replaced with a known working one
most common ones are faulty MAF (doesnt always throw a code but i can tell when it's gone usually), coil packs, leaking DV, loose pipework to the intercooler, split vac line which can take forever to trace, and today's favourite was a perished 'Y' shape breather that comes out the top of the cam cover. Mine has a tiny hole in it but the customer's car today was broken in 3 places.. all the way down to where it exits the block by the dipstick! ... grazed knuckles again for me