Introduced in 1998, the Volkswagen Beetle TDI can suffer from a number of common problems that can often be resolved via some basic troubleshooting techniques.
The VW Beetle TDI can experience loss of power due to the accumulation of carbon, soot and oil in the intake manifold, which sends air to the engine cylinders. Remove the intake manifold gasket, clear out the sediment build-up in the manifold with a scraper and install a new intake manifold gasket.
The MAF (mass air flow) sensor measures the air that flows through the throttle body and intake manifold. When a MAF sensor goes bad, the results can be poor gas mileage, engine knocking and/or engine hesitation. Check the MAF sensor for signs of damage (along with the wire connection for looseness or corrosion) and make the necessary adjustments or replacements.
Injection Pump Failure
A VW Beetle TDI running on biofuel can experience fuel injection pump failure, resulting in the inability to start the engine. Inspect the injection pump for leakage around the delivery valve retainer screw and tighten it as needed. Also check for a worn governor, worn governor linkage or damaged transfer pump blades and replace them as needed.