Your BM should have break in by now? if above 10k kms?
Or you always sayang2, drive slow slow, this is diesel car lah, so sometimes on straight h/way (when you are alone - for safety reason) hantam hard & fast to say 160-180kph - my idea is to "blow off the deposit on the fuel injection nozzles" - no jokes! maybe it helps? some cars really need to beat them before they perform, I remember an Alfa I used upteem years ago, if always drive slow slow in jam - it choked! so have to trashed them hard & fast every weekend to smoothen, or once have a chance on h'way.
Also try a can of blue chem occassionally - available at Cergazam PJ SC to clean nozzles, try also their Xado and see how it goes? MY BMs they just put for me without asking - always they bully me - so I try all things and I told them I hope the engine blow and they claim a new engine for me!
For my 2 Bms, even how hard it was trashed I get above 600 to 680km/100RM
The traffic you experienced last Sat is quite normal in Cheras, considered peak hours. However i'm lucky to avoid most traffic on daily basis, with the help from some short cuts i.e. not driving as fast as in H/Way.
Will try out your suggestion to de-carbon my BM. NS H/Way is still the best road to do that. Some friends even suggested to add in cooking palm oil (approx 10ml to a full tank of diesel) as nozzle cleaner and lubricant. That sounds logical as home made B5 diesel. Will continue monitor the FC.
Lastly, I'm happy because I got extra power, and FC remain unchanged, consider untung oledi.