My Auto Hyundai i20 revs extremely high when I accelerate as if the clutch was in when changing gears without taking your foot off the accelerator.

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Question moved to model category.

It sounds like you have and unusual and flawed driving technique.

Manual or Automatic?

Automatic. You never use neutral unless you are in a car wash that drags your car by the wheels. Decelerate, foot on the brake and into Park. Your right foot does both brake and accelerator, left foot does nothing. I saw a lady 2 days ago with left foot on the brake and right foot on the accelerator.

Manual. Downshift through the gears, right foot on the brake, left foot on the clutch and into neutral and hand brake on.

If you are doing that, the vehicle needs diagnosis why it is happening.

Yes, it is a known issue

https://www.google.com/search?q=vw+jetta+2.0+tfsi+rev+hanging

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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

is it auto matic or shift . if shift its clutch judder oil on clutch plate

Check for a vacuum hose leak

clutch is slipping you will need to replace the whole unit,plate/bearing/friction .

possible issue with the clutch plates....get them replaced.

You need to check the cable the runs from the gas pedal to the engine, it might be rusty and need some drops of penetrating oil at the point it meets with the engine accelerator valve.

This is a very common problem for ford. I have the same thing every day. It is the computer not reading the temp. When it does that just tap the gas pedal.

The grinding sound may be a throw out bearing or the pilot bearing. The sticking throttle problem sounds like a linkage or cable binding up from possibly damage due to the impact from the accident.