207 RC power drop and very low manifold pressure

[Ventori]

Hello, at first i would like to sorry for my English, but it's not my national language. I decided to describe my problem at foreign forum because my local ones has out of ideas for my issue. In short; i was in two different roling roads and my THP175 has ~140hp and i have two rpm drops, always at specific range. First between 3000-4000 and second at 4500-5800 according to the chart from rolling roads. One of the tuner said i have too lean AFR (which is ~14.4) and i shouldn't drive with this afr because it may cause irreversible consequences for the engine.

Previous owner did:
cylinder replacement including checking and planning + new valve sealant + crankshaft simering
new spark plugs (2018)
new turbo water pump (2018)

I did so far: (since 2019r)
engine compression is ok
intake valves cleaned using "walnut blast" method + my mechanic advised me that i should add oil catch tank so i did
all sensors checked
new ignition coils
new high pressure fuel pump
new timing gear (im 100% sure it is well mounted, camshaft checked and it's well set), my mechanic used genuine camshaft locks for thp engine. He showed me live how he used camshafts locks, to prove that the timing gear has not changed.
new valve cover (old one caused some oil leaks)
changing oil and all filters + engine flushing

I don't know what else i can do, mechanics spread their hands. The only guy left i can trust (who exchanged my timing gear and knows thp engine) says the problems is in cylinder and i made an appointment with him for March for cylinder repair. (March is the nearest spare date) This mechanic deals with the repair of 1.6 thp engines on a daily basis.

... waiting for the March visit i decided to call a visit to nearest Peugeot authorized service in Poland
They're said there's no fault codes. They made a test drive and feels those "power drops" but couldn't exactly tell what causes those power drop.
I asked them about my turbo because tuner earlier said it loading 0.2bar less then it should but mechanics from ASO said that according to their computer, the turbo is ok. The only thing they were worried about was too low intake manifold pressure, the set pressure was 30mbar at idle but the correct values are 250-350mbar. I'm sure the sensors is ok because i swapped it earlier with my buddy's THP. Do i need to buy a new factory manifold intake? or what else should i check / replace?

And one more thing they noticed that my Turbo Air Hose Pipe is a bit damaged (rupture near cold side of turbo). I gonna buy new one. At the end of servicing in Peugeot they told me they will send gathered data to the main central of Peugeot and they let me know when they find out something.

I will be grateful for any help! I want to finally get this car to its factory condition and make ~200hp remap.

[xantia_v6]

It is difficult to diagnose this problem without having more data. It would help to know what the manifold pressure (set point and actual) is at the RPM bands where the power is low.

I presume that the measurement of lean AFR was made with an external instrument, it would be useful to know what the engine sensor was reading.

Do you have access to a Diagnose diagnostic tool? Can you read the mixture trims and timing trims?