yes, guys the problem is now solved.
the simplest repair I've ever done.
An MB mechanic friend from the Philippines just told me to clean the throttle valve (the round thing that flaps to let the air in). I removed the air in-take tube and had a look inside and true enough the outer part had accumulated some carbon/dust deposits. Sprayed it with a carburator cleaner, wiped it out and voommmm.
I've been driving it for 2 days now and that idling problem hasn't showed up again and in the past a day won't pass that idling will be go down to 450-500 rpm.
.....just so smooth.