Citroen C5 2.0HDI increasing RPMs in Idle

[coa]

Hey, there community,

I have been having the same issue with my Citroen C5 for 2-3 years now.
It is driving without any issues, it has enough power, but the issue of iractic idle persists.

Car Model: Citroen C5, 2009 year, 2.0 HDI 120KW - 163HP, automatic transmission

When running in idle the motor RPMs are increasing to 1200-1300 RPMs. If I shift to a gear, and if it raises rpms, the car will start moving (forward or reverse doesn't matter which gear).
When I press the Brake, RPMs immediately drop to regular 900-1000.

So when idle, it's increasing rpms, and when pressing the brake it's stopping it.

I have regular maintenance, a new battery. Have been to several mechanics, and electronics, and got different suggestions, so far we tried the:

Replacing new gas pedal, turning off EGR, removing FAP filter ( it was clogging a lot )(ps my country is not in EU, so I kinda get to pass the yearly technical review).

Diagnostics are reporting: regulator for fuel pressure, and something with injecting system.
The second one turns the engine lamp from time to time (mostly city drive), and when the engine lamp is turned on, only then the inject issue is seen in diagnostics.
If the engine lamp is off, only the regulator of fuel pressure is present in errors.

Have been going to 10s of mechanics and shops, but no one could figure out what is the issue really about.
Some local guy, who specialized in fuel injection systems, told me that it couldn't be the regulator of fuel pressure, as it behaves very differently, and that I would have different RPMs increasing when driving, to much higher values - not only in idle. He said, that since It is increasing RPMs only in Idle, it should not be the regulator itself the issue. Not sure if I should trust him tho.

I spoke to several people who had similar cars, different motors, and different transmissions, and few of them had the pretty much same problem.

Additionally, I read that changing the spark plugs could fix the issue, some other suggest that some vacuum system is loose, or brake vacuum system.

Since I am out of options here, I am really looking forward to your help.

[RichardW]

Welcome!

The 1200 rpm and idle drop back when brake pressed is the default strategy when there is no (or incorrect) signal from the throttle pedal. You need to look in live data and see what it is reporting. If you have changed the pedal already, then you might need to start on the wiring next!

[coa]

Anyone, any new thoughts?

Its not throtle pedal