The MAF is located directly under the air filter assembly, which is the large rectangular box at the back of the engine bay with a long air intake tube at each end. To get to the MAF, remove the two long air tubes. Release the four straps that hold the upper half of the box to the lower part. Lift the top cover up slightly at the right hand side, it will not lift far due to the hose which connects underneath, from the air pump. (RHS here means facing the front of the car from the driver's seat) A worm drive clip retains the hose. Undo the clip and pull off the hose. Remove the upper housing. Then remove the air filter, keeping it upright. Note or mark its top face so it can be replaced the same side up. Turning it over may deposit debris into the engine !
On pre S4 cars, two 13mm hexagon headed bolts secure the lower half of the air cleaner box. They are captive in the lower half, so will not pull out when fully loose, but it will be obvious when they have been fully unthreaded. Lift the lower half up, the MAF will come out of the throttle casting with the lower half of. Do not lift it by more than a couple of inches, as there are leads connected. There is a 2-pin plug connected to an air temperature sensor on the underside of the housing. Disconnect this by wriggling it from side to side while pulling. Only pull the plug, never the wire ! Then disconnect the 6-way connector on the MAF. The lower housing half complete with the MAF can now be removed from the car, and the MAF taken off by releasing the worm drive clip.
On the early 5 litre USA "86.5" cars, the lower half of the housing is held by one 10mm bolt each side.
On all the later cars from 1987 onwards, the lower air filter housing is held with two 10mm bolts at each side. On these cars the MAF will remain in the rubber elbow connecting it to the throttle housing when the lower casing is removed. The MAF is held in the elbow by a worm drive clip, which is a little tricky to get at. Use a 7mm spanner to undo the clip drive about one turn. The MAF can then be eased out of the elbow and disconnected.