Do you know what the fault code actually is? An Implausible signal error is likely to point to a wiring fault, while a "too low" error is more likely to point to a problem elsewhere (though you can't rule out the possibility that the new one is faulty too).

If you put your error code into Ross-Tech's website it will usually give you a list of things to check, some of which you may not have thought of...

 

Sounds like that it's failing a plausibility check between the MAF and another (inferred) measure of airmass (probably from speed/density - uses engine speed and manifold pressure to estimate airmass) if there's a big enough difference then it'll set a flag and dash light as the sensor signal cannot be relied on - its an emissions thing.

I would check for air leaks have you made any changes or had any new parts fitted or check for missing or split vacuum/pressure hoses, split induction parts, missing or loose breathers, leaks in the exhaust, loose clips. I don't have much (any) specific knowledge of these engines so can't point you to actual parts, but have experience of engine and powertrain diagnostics.

 

HI, have the very same issue on a 1.9 '07 van, new MAF and still coming back with implausible flow fault, or something to that effect. Beginning to wonder if theres a break in the wire from vibration or vermin!!?
Started off with egr excessive flow code (1026) & boost pressure regulation (0665) fault code, but sorted those cleaning out egr & fitting a partial blank off plate......
If you've resolved your maf issue or had any more thought, i'd appreciate a reply....
Cheers mark