Anxiety on TOYOTA Caldina AZT-241W

I have an anxiety on my TOYOTA Caldina AZT-241W, it's blush wear, at the time 2 years ago, the alternator was disassembled to  confirm the condition of it, I regarded the life should be 30,000 km use, now the decided distance is covered already. In spite of such kind of danger my vehicle has, the work has been postponed as hesitating, coldest season now is the reason. Replacement parts had been obtained already, just sabotage.
It would be done at any rate some sunny and warmer day ASAP.
As for the starter motor, one of 4 terminal blushes was worn out unreasonably, but more 50,000 km use will be continued, so I believe.
The problem that happens suddenly while idling of D4 motor, it is often the case on D4 motor among the users appears on my Caldina without exception.
As some experimental trial, I tried to run keeping 4000 rpm for about 1 hour on the highway, then the strange phenomena disappeared thoroughly and smooth, powerful and stable operation were reacquired again, low speed and dull driving condition must have piled carbon and sludge in the valve construction?
Because the motor mounts were replaced after 150,000 km use, I would like to continue this one more 30,000 km without any trouble, my lovely equipment.