Toyota have installed these round filters on all turbo diesels to keep oil out of the MAP sensor. The OEM items ( part numbers 90917-11036 and 90917-11044) are plastic and has a reputation of cracking due to age and pressure (potentially higher than standard).
The PDI stainless filter is fitted with the same felt pad as the factory unit, and has been assembled with laser welding for a perfect seamless product.
Why do I need one?
Power will be compromised if the MAP sensor can’t measure the boost correctly as fuel delivery is done based on boost.
For common rail engines fitted with VNT turbo it is vital there is no leak in the line between manifold and MAP sensor. If the ECU is unable to correctly read manifold pressure, the vanes will be closed to assist in building pressure and this situation can cause the vanes to melt.