Multiple diag codes - what do I fix first - Help!

[ex_directory]

My 17 year old son's car 2004 Polo twist has recently had a engine light come on, diag reports CAT problem P0420.

Did an emissions test and all seemed fine so cleared code.

While ignoring it for last couple of weeks engine light came on again, tried to clear it by disconnecting battery (did not work).

Next day, car started rev hunting, and going around corners could stall etc. EPM light comes on sometimes. Other times car starts fine and drives fine.

Today, did diag and new set of codes though now being reported:

P1565 - Throttle actuator
P1579 - Throttle body related
P0106 - Manifold pressure sensor related
P0172 - Fuel too rich?

Garage are asking me what I would like to do!?

Suddenly in to scary territory with cost, but could one of these problems be triggering the others?

Please help!

[niall campbell]

VAG Error Code: 16804
EOBD II Error Code: P0420

Fault Location:
Catalytic Converter System, Bank 1 - Efficiency Below Threshold

Possible Cause:
Leakage in Intake and/or Exhaust System.
Catalyst faulty.
Oxygen Sensor(s) faulty.
Oxygen Sensor(s) Control faulty.

Possible Solutions:
Check Intake and Exhaust System for Leaks.
Check Catalyst.
Check Oxygen Sensor(s).
Check Oxygen Sensor(s) Control.
Perform Oxygen Sensor(s) Aging Check.

Is the pipes leading to air filter on ?

the oxygen sensor may be faulty if the fuel mix is too strong ?

is the air filter clean ??? I would replace the air filter for a new one for a start

[Crasher]

Remove and thoroughly (but gently) clean the throttle body, it will be solid with EGR deposits on the back, use an aerosol carb/injection cleaner and stiff nylon bush, you must not scratch the bore or butterfly edges. Then the TB will need re-matching to the ECU which is done in Basic Settings 060 with a diagnostic system such as VCDS.

[ex_directory]

Thanks for your help.

Had the throttle body cleaned and the ECU recalibrated, for now this seems to have done the trick.

While doing this the garage found a split in a pipe, although it is not clear which pipe or what it was doing and if this is related. Anyway, this has been replaced.

We changed the air filter not long ago so this should be fine.

I have a feeling the engine light will come on again soon, let's see what the code will be!

[Crasher]

Probably poor catalyst efficiency caused by over fuelling due to the air leak that has now been fixed.

[ex_directory]

Confirmed it was an air pipe that had a split. Still no light. Keeping fingers crossed.

Thanks for help.