hi guys,
this one has been giving me lots of dramas as i cannot pinpoint why it happens.

sometimes engine either idles too low or too high, so i set it correct again , then it is fine for an unknown amount of time, maybe a day maybe a week, then suddenly whatever i set it to changes again.. say it was too low and i increased it , few days later now it is too high...
or it was too high and i decreased it, few days later it is too low..
in above cases engine works normal but idling varies for unknown reasons.

then less occasionally engine idling goes erratic.. tachometer moves up and down erratically then engine stalls and dies.. at this stage engine also blows black smoke. after sometime and not necessarily by engine getting hot, it stables on it's own.

according to receipts from previous owner car had the same problem and attempts to fix it were
replace faulty idle speed motor, check engine operation
which didn't fix the issue then later on
-found idle speed motor o-ring distorted, replaced
-clleaned idle air bypass back passage
-cleaned throttle body
and invoice mentions oil burning due to valve stem seals.. but i see no blue smoke at all.

again it didn't fix the problem.
when i bought the car and faced the same issue and plus at times car just didn't want to accelerate i did
-used 6 packs of injector cleaner, starting with the expensive full fuel system cleaner then few bottles of normal injector cleaner.
-cleaned maf sensor
-replaced front spark plugs
-replaced a dodgy spark plug wire
-changed all belts, timing belt, tensioner, etc water pump
-found a small vacuum leak and fixed it
-replaced fuel filter

these relevant or irrelevant measures didn't entirely fix the issue but greatly reduced it's occurance.
yesterday, i did some work inside the car installling stereo system, and kept the engine idling to get aircon.. over an hour of idling and no issue at all.. then i t urn off the engine do some work at home, and decide to go out for shopping eetc... and engine goes crazy again.. for over 20 minutes struggled idling, stalling even brakes not working at times then it stabilized again.. today i drove the car no issues at all..

my mechanic who did the belts and pump, didn't notice any abnormalities with the engine...

here is a video from yesterday
https://youtu.be/fMeaUgZrXDQ

i don't know what else to do.. rear spark plugs maybe due replace but i can't get there yet. i thought fuel system and injectors might be dirty.. hence used the cleaners.