My 2001 vw passat 1.6 petrol failed nct. Emissions low idle and high idle too high

Cut them off is the simplest way but you must remember that you have o2 sensors that control your engines emissions and may affect the exhaust (emissions/smog tests) and by removing cats you check engine light may come on as a result so be cautious of this...

might check the catalytic converter and sensors. I had the same problem and had to replace 2 catalytic convertes in the front of my 2001 VW Passat wagon.

You need the codes pulled form the vehicles ECU with a scanner. The TDI engine does not do this when running correctly.

There are a number of reasons I can think of why this might happen, some being, Glow Plug/s failure, injection pump problem, such as temperature sensor failed, fuel system air leaks and alternator charging problems..

The alternator has a one way drive pulley that fails often causing unstable idle and belt noise..

Low power indicates the engine is in limp mode needing attention.

Find a garage with a scanner for this VW and allow them to check the vehicle.

the O2 sensor works on one volt .5 is around the running voltage, i would refit the air hose as it will run the converter hotter at idle.

Did you install new spark plugs? Definitely replace the O2 sensor.

Idle is automatically set&monitored with a timing sensor on the camshaft, i found my engine(1.8 20v turbo) would idle low then go high and almost stall sometimes and all i did was remove the fat black pipe on the throttle and clean inside the throat with a cotton rag dabbed in wd40.Hold the throttle open manually and clean on and around the throttle plate as the oil burnt&recycled creates a hard carbon that stops the throttle working correctly.When did you last change the sparkplugs, air filter, oil and oil filter and remove damp from the spark plug area using wd40 on surfaces applied with a cotton rag.These contribute all to your problem.As you dont state milage etc it could be a worn engine or slipped cambelt(1-2 teeth can make a slight diffirence).

vaccum leaks cause this type of misfire . this sometimes happens when someone works on car and does not tighten hoses also could be low fuel pressure or lean fuel caused by air to fuel ratio. i would try vaccum first

sorry if that is the code it is not correct with the obd format it surpose to have something like P0033 re-check and let us know the correct code

That sounds about right, the idle speed may not even be manually settable due to emissions regulations.
I know for sure you can't adjust the idle mixture anymore; that is determined by sensors and the on-board computer.
There may still be adjustments on some cars but they are often sealed with lead to avoid tinkering.