in that case its going to be a lack of fuel so either the ECU isn't opening the injectors enough or there's not enough fuel pressure ( hence my suggestion of measuring it at the injector rail)
This could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for causing rough running.
As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.
Check the hoseclips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.
The best way to locate a leak is to have the engine running and warm and then spray lighter gas/propane around each joint in turn. If the engine rev's up you've found your leak.
Now you mightthink that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.
Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can oflighter gas to provide a spraying 'wand' and allow a direct blast of gas intoeach area, especially those difficult to reach with large implements.
Might also be worth checking the wiring and connector to the airflow meter for any signs ofcorrosion or damage. you can do a quick fault find if you unplug the meter andrun the engine without it.
if the engine condition is the same then chances are the meter or the connection to it isfaulty
It’s also worth cleaning the MAF sensor wires, as they can get coated with dirt over time which then offsets the reading
Use some contact cleaner or brake cleaner to spray onto the wires to remove the dirt – on no account touch the wires with anything as they are very fragile