How do you change a camshaft position sensor ?

Sounds like faulty O2 sensor or bad wiring to it

A sensor dirty or faulty most likely, usually is with C2's, lambda sensor.

engine ecu has fault codes to be read

several parts and sensors cover anti polution problems

The computer has detected a problem with the emission system on the vehicle. Start by checking your gas cap is on and tight. Have a look under the hood for any disconnected hoses especially around the air filter assembly. The vehicle may have to be scanned to properly diagnose an emission fault

anti-pollution faults come from incorrect emissions from the exhaust or problems with the canister system. I would be getting a second opinion of the fault codes before I spent money there.

Could be the camshaft position sensor. It works with the crankshaft sensor to set timing. You can remove it and clean off the flat tip. I have seen metal filings on them that causes timing problems.

service the car fully, including pollen filter

car keeps on slowing down, when iam driving and changing gears.

anti pollution fault with fault codes poo87 poo93 i changed fuel filter, so far all ok.

P0340 FORD - Camshaft Position Sensor Circuit Bank 1 Sensor 1Possible causes- Faulty Camshaft Position Sensor
- Camshaft Position Sensor harness is open or shorted
- Camshaft Position Sensor circuit poor electrical connection
- Faulty starter motor
- Starting system circuit
- Dead (Weak) battery
P0340 FORD Description The Camshaft Position Sensor is an electronic device used in an engine to record the rate at which the camshaft is spinning. This information is used by the Engine Control Module(ECM) to control ignition and fuel injection. The camshaft position sensor senses the retraction of camshaft (intake) to identify a particular cylinder. The camshaft position sensor senses the piston position. The sensor system consists of a rotating part, typically a disc, as well as a static part, the actual sensor.

When the engine is running, the high and low parts of the teeth cause the gap with the sensor to change. The changing gap causes the magnetic field near the sensor to change. The change in the magnetic field cause the voltage from the sensor to change.

When the crankshaft position sensor (POS) system becomes inoperative, the camshaft position sensor provides various controls of engine parts instead, utilizing timing of cylinder identification signals.
P0430, main catalyst is worn out.