I brought my problematic Canon EF-S 18-55mm lens to a camera shop on Sunday to see what's wrong with it.
The technician said that there's some internal problem with the aperture, and to service it might cost around RM300 or more, since the spare part for this particular lens is very expensive, compared to the newer IS version of this lens. So I decided to look at other options, probably sourcing a 2nd hand lens to replace this one.
The only incident that I think could have damaged the lens would be during Hobbycon 2010, I forgot which day it was, but there was one day when I took my camera out of my bag, and was fiddling with it, but it slipped out of my hand and bumped onto the table, which was about a one-foot drop. I immediately switched it on and made a few test shots that time, and it seemed to be functioning well.
It only had major a major malfunction when I took it to Kuching after Hobbycon. During that time, it was spotty, sometimes it worked, sometimes it didn't. Luckily I brought along my 28mm F/1.8 along on that trip, or else I wouldn't be able to snap anymore photos. During the rest of the trip, it didn't seem to be malfunctioning, so I just let it be.
The problem manifests itself when I select an aperture that is smaller than the maximum aperture for that particular focal length. For example, the maximum aperture at 18mm is f/3.5, so if i were to set the aperture to f4.0 or above and shoot, the lens would crap out and my camera would complain, saying that there's no communication between the lens and the camera body. Initially I tried all the "clean contacts with eraser" methods but it still would not solve the problem, hence the visit to the camera shop.
Anyway, I'll have to see where I can source for a replacement for this lens, since I was planning to sell it off with my old camera body.