I think my D5000 (or lens?) AF is malfunctioning, but I'm not sure. I'm using the stock lens (Nikon DX, AF-S NIKKOR 18-55mm) It takes seconds (like 7 seconds) for it to find focus and seems to keep going back and forth in and out of focus. I can see the lens/image and hear the motor move it in and past focus to back in focus and it goes several times during focusing. It kinds of does like a quick search on focus then small adjust then a large adjust then fine adjust and finally decides and takes the picture. This is even with a tripod and still shot, i.e., it shouldn't have to change focus decision. Sometimes it seems to stop with no part of the shot in focus. Note I also typically have VR off not sure that would make any difference though.
My other thought is that I hadn't been using it much for a while, so I'm also not sure if this was the normal focus behavior. I'm not sure if cleaning would be appropriate? I haven't physically cleaned the sensor. What I end up doing to work around is MF, AF and flip to MF, or AF and not release the shutter button fully.
I'm not sure if this could be just a setting? I don't think I've messed with the focus settings other than switching from AF to MF or locking the focus.
I'm missing lots of action shots unfortunately.