High Idle - Rmp meter not working?

Hey,

my car:

Citroen Berlingo 1,4 1997.

For some weeks ago, my Rpm meter ( tachometer ) started to have some problems. Some times when i started my car, the Rmp meter did function and some times it did not. At the moment, it have not been working for about 2 weeks. And now my engine Idle speed is very high. Its so high that i can drive in 2. gear without touching the accelerator pedal.

Estimated idle speed is about 3,5K to 4K ( Or even higher, hard to tell )

* When i start my car, regardless of Cold or hot Engine. My Idle speed is normal for about 5 sec then it will slowly go up.

* If i push the the accelerator pedal and then release it, the engine will stay at the same Idle speed as i had when i pushed the pedal.

* I have checked the gas cable, its OK

* I have checked the Throttle Body. Seems OK.

* A local Citroen workshop tryed to find the problem, but they could not get connection between the computer and my cars brain. So they was not able to help me at all. ( they told me to check the fuses, but every single one is ok. )

I think that the tachometer has two functions. It tells the brain what position the flywheel is in and provides information to the tachometer. I tried to disconnect the sensor, but then i cant start the car.
Is it possible that one of the function of the sensor is not working as it should?

I would also mention some other problems that I have not noticed until now.

When i turn on the ignition, I can then hear my fuel pump running. The only problem is that it just keep running. I believe it should run for about 5 seconds and then stop.