RPM's not raising when throttled down and not moving

Okay, you disconnected the battery to change the pump and such correct? Now it does not want to idle or move when you put it in gear?
That sounds like it needs the throttle body cleaned, then it needs to relearn idle in and out of gear. Disconnecting the battery erases all of the learned values. The computer then goes back to the baseline numbers. If the throttle body and idle control are dirty the baseline will not let it run because of the crud. So I would start with that, then start it and drive it around.

Thank you for your reply. how can i locate the throttle body, and also erase the learned values?

Not to sound like I'm demeaning you but unless you have cleaned a few throttle bodies before I wouldn't want this to be the first. It is easy to damage one and this one is VERY expensive (over $2,000.00). I would say this is an instance where taking it to a shop and having them check it would be a prudent step.

Here is a guide on a much easier vehicle to give you an idea of the process.
https://www.2carpros.com/articles/throttle-actuator-service

thank you Steve for the answer, that is for cars with injector, Clk320 1999 Doesn't have that injector, what do i do in this case

Which engine do you have ? Diesel or gas?

Petrol engine

Then you have a throttle body and injectors. The one in the video was not your make/model, it was just to show how the throttle body can be gunked up and cleaned. Sorry if it was confusing.
Yours is M16/6 in these pictures. There isn't a video guide for that exact vehicle which is another reason I suggested taking it to a shop.

Thank you, Mr Steve, i was able to clean the throttle body, it was raising but not properly,
after changing the air flow meter it was better and sound...am so grateful

Good Job. Thank you for using 2CarPros.com Come back anytime with your automotive questions.

it has gone back to the same issue, this time around i changed the throttle body is not yet responding ,what can i do

If changing the TB out didn't change things then the issue will be to watch the fuel pressure and ignition to see which is causing the problem. That may take some dealer level testing. Do you have a factory level scan tool to watch the fuel trims and timing vs engine loading and rpm?

The fuel pressure was tested, the pressure is perfect,The mechanic i called said it may be the brain box, i don't know. Don't have a factory level scan tool....
comes on perfectly well.

This car will go into limp mode if you have a vacuum leak somewhere in the intake system or intake tube. Here is a guide to help you confirm the issue.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Please let us know what happens.

Cheers, Ken