Less power and pinging down low

Hi I have a 97 sportage which once drove fine, its dont about 130k and all of a sudden lost power (still drivable but lacks power) I since have had the car serviced and changed plugs\filters etc. Still lacking in power. Checked puel press, it seems to be ok.
I am thinking timing could be a little off? But I was told that these cars dont have adjustable timing? I dont beleive that and think the mechanic is having a lend of me. Where can the timing be adjusted from and what should it be at?

The car also sometimes pings down low in the rev range.
Yet at other times, the car seems to run fine.
I have used both standard fuel as well as premium fuel, also added fuel injector cleaner into the fuel etc.

Could this have anything to do with the battery getting old? It always starts fine but sometimes sounds like the batterty is on its way.

Any help would be appreciated.

Cheers

Do you have the Check Engine Light ON???
NO! battery is out of the question. ANd YES, timing is indeed NOT user adjustable: computer does it. Could be knock sensor. If it fails, computer falls into a default mode and retards the timing to avoid pinging....what surprises me though is why it would still ping?...ANyway, best is to have the codes checked : codes are not a "live or die" information...but sometimes they help.
Once this is checked out, we can look for more complicated things.
Are you sure of the fuel quality? No diezel fuel by mistake? Diezel fuel causes a LOT of knocking and the computer would retard the timing way back....
By the way...was the timing belt changed yet? IF not...it is WELL overdue......since 70kmiles....and jumping one or 2 cogs on the belt would certainly explain the sudden power loss.........this would be my best guess.......and this does not light up the CEL....

Thanks for your reply, The engine light comes and goes. We checked the codes a while ago and it was indicating the knock sensor. The mechanic took the sensor out and cleaned it and reinstalled it and this made the light go away. Could it be that the computer has this in its memory?
I think the timing belt has been done and diesel hasnt been used.
What do knock sensors usually cost.
Cheers
Ben

rockauto.com lists the knock sensor at around $100. check on e-bay at 68...+ freight and handling..
THe sensor is an electronic device, in fact, the equivalent of a crystal microphone; some have the filter or signal conditioner built in , others have an external filter (to sort out the right frequencies); electrical contacts at the plug are to be checked out but otherwise general cleanliness is rather irrelevant....
Troubles that do not reappear will generally erase themselves out after a given number of engine cycles , so if the code is still there, it is probably recent.