Land Rover Repair: 02 Freelander HSE - Service Engine Soon Light, mass airflow sensor, mass air flow sensor

Question
Have a 2002 Freelander HSE with 90,000 miles.  The Service Engine light was on and there was a significant decrease in acceleration.  Took it to a local mechanic who said that the  catalytic converters needed to be replaced.  Replaced both including 4 oxygen sensors.  Could not clear code P1471 and occasionally P1472.  Replaced Mass Airflow Sensor.  Code P1471 still would not clear.  Removed engine cover, including the intake air filter.  Car ran great, no problems.  P1471 code cleared and service engine soon light stayed off.  Replaced the air filter with a high performance air filter, attached to the Mass Air Flow Sensor.  This seemed to solve the problem for approximately 20 miles and then the Service Engine light came back on.  What's the problem? Can you help?

Answer
The 1471 and 1472 codes point to problems in the variable inlet system.  The vehicle needs a new intake manifold or new manifold motors and plates.  LR sells a motor kit but at least half the time the kit does not work and you need the whole intake anyway.  The other work you did would not address a variable intake fault code.