Revs whilst moving

do they revs drop off when taking pressure off accelerator pedal when out of gear? if only staying high during gear change it would suggest a worn clutch friction/pressure plate so the engine isn't slowing down when clutch is depressed .I'd also have the OBD codes read to see if there is a sensor/switch at fault , but sounds like the clutch to me

sounds like it needs a new clutch theres no way around it your letting out the clutch fully before it moves at high revs your clutch is burnt out it only works better when its hots because its expanded by the heat but when its cooled down it wont move again yep its a new one.

If I am hearing you right, the engine revs ONLY when the clutch is depressed?
I would have to doubt that is what is really happening, tho. Is it possible that the engine is revving from the time that you start it, until the time that you shut it off?
This would be more likely, as depressing the clutch doesn't really have any effect on the engine, other than dis-engaging the drive-line...
IF it is revving at start up, see if it isn't only 'idling down' when the weight of the vehicle puts a load on the motor. In other words, does it idle down, or does it only SEEM like it is, because now it's pulling the car? Do you have to give it gas to go on a flat surface? If not, then it's still revving.
Then, if you decide that it's revving ALL the time, you will need to check it for vacuum-leaks or mis-adjusted linkages, or carburetor (throttle body, if it is injected).
Do yourself a favor and buy a Chilton or Haynes manual for your vehicle (at most any auto parts store), if you plan to keep it for a while. They will generally have troubleshooting sections, to help you eliminate variables until you find the actual issue. It's the best $20 you can spend!

gearbox not done correctly. gears tight

Your clutch needs to be replaced.

you are having an air leak. as for water in the bottom chamber of the intake its supposed to be there. air has water in it. if its water in the injection line then its down to were you get your fuel. if you are losing compression it would be down the the valves or piston rings, or a failing egr valve. can also be the wrong spark plug gap. and in some case it can be the clutch. to test clutch put in 3rd gear and try to take off if it dont move but engine revs up then it will be this. only do this once as any more times you could warp the fly wheel.

you car is fitted with a "no fuel"system,so when you take your foot off "no fuel" goes to the engine untill it reaches 1200 revs.then it will allow fuel to flow to keep tickover/smoothness.(its computer controlled)you need to get your car onto the diagnostic computer,(skoda/seat/vw/audi)so you have the codes/items that need to be sorted.The tdi engine was one of the first engines that VW computerised and it is very reliable/powerful,compared to the peugeot/citroen engine.(briefly,the fault is not just a switch/cable),

it's not if you have hydraulic system.
check to see if the clutch pedal is firm and has pressure
start your engine, depress the clutch pedal and put it in gear
if it goes in gear easily and the car won't move then you need clutch

the vacuum booster forthe brakes has developed an internal leak, disconnnect it plug the hose and repeat the test, if there is no change in revs you have the solution

check the gas cable at the throttle body under the hood, it is possible the cable has either broken or become dis connected. remove the air cleaner and look into throttle body and find the rotating shaft that opens and closes the plate inside throttle body. 1) when you rotate does plate move? 2) is there cable attached to pulley? 3) when someone steps on pedal does the plate move? 1 not likely issue, 2 might be issue reattach cable to pulley, 3 pedal does not move pulley cable disconnected at pedal reconnect there or cable is broken replace cable. if non of these then throttle position sensor may be bad and check or replace