plugging in the scanner does not necessarily mean you check for fault codes. i could have done that yesterday when i checked the car by plugging in the connectors. i want the see the live data of the engine sensors. to what i saw yesterday was, the idle being rough intermittently and not lumpy as described. no vaccum leaks were detected after blocking off the bov and its lines, problem was still there. i checked the spark plugs, which was near new, leads were within specs except for number 4 which was showing intermittent values and low reading ( i did replace that ).
cleaned the afm, isc valve as well. did an upper engine clean, was better for a while than it started again. drove it and felt no power from the turbo. car has aftermarket equal length headers, up pipe, vf22 turbo and catless down pipe.
so what i under stand at this stage is that one of the sensors could be a bit lazy and giving a wrong reading. i will be able to confirm this by reading the live data while the fault happens. it can be any sensor related to idling that can cause this rough idle.
will update tomorrow of the findings.