DS3 Petrol - holding back / slight juddering at high revs

[Jaseomar]

Hello everyone , first time post - long time driver (sufferer) of numerous cars over 35 years.

Citroen DS3 THP Dsport 9 years old 65000 miles. Clean nice little car. had it 6 months but it's developed a power delivery problem "holding back" slight juderring most noticeable at higher revs. Seems worst in 3rd gear. Local garage has tried loads of things but to no avail.

No warning lights, given it new coil packs, spark plugs, fuel cleaner, injector cleaner, Turbo Pressure 1.2 bar, Fuel pressure normal, injectors testing fine, timing in normal parameters, Compression test good, drained fuel and check tank, Sensors checked (Map, Oxygen, Airflow) - can give more details on some of these things.

NOTE - I am reliant on garages/mechanics/friends for sources of information. I have some knowledge but no loads.

ADVICE / QUESTION. One main garage suggesting engine coked. One local garage wanting to investigate timing chain. I'm not convinced of either of these things will find the actual fault. Has nayone else had this problem / resolved it. Thank you and Merry Christmas

[PaulC5]

Have you tried a Citroen dealer with their diagnostic equipment ? Also there might be a fuel filter, has that been changed.

[Jaseomar]

Thanks Paul One main Citroen dealer didn't want to check the car because he felt it would be too expensive (to him) to diagnose the fault. They were suggesting engine might be coked up.

The original garage (where I bought the car) did inspect the fuel filter but didn't change it. It's a pain to change being at the bottom of the fuel tank. That garage I think have stopped trading now so I can't double check.

[PaulC5]

Some things to read viewtopic.php?t=84296

[myglaren]

There may be something in the engine being coked up.
I can't recall which but they were shared with BMW and had the propensity to choke the valves and inlet manifold with coke.

IIRC blasting with hazelnut shells was the cure. Hardly cheap I imagine.
A borescope may confirm that.

[Jaseomar]

haven't heard about a borescope that's got to be a whole lot cheaper than taking top part of engine off. I'm guessing I should go to a main dealer to try this? There's quite a list of things to check if there's a suspicion of carbon build up, valve timing, cylinder leak test, blow by, vacuum test. Need to ask garage about these things too