MAF (Mass Air Flow) sensor for VW TDI Jetta, Golf and New Beetle TDI on the A4 chassis with engine code ALH.  Manufactured by Bosch
 
A bad or failing MAF can result in low fuel economy, low power and "limp mode" where the car loses all power until restarted.
 
This is the updated revision featuring an internal baffle/air restrictor to protect the sensor. This will last longer than the OEM sensor and is currently the best mass airflow sensor for your ALH TDI.