Hello, I have a 1990 toyota corolla with a first gen. 4a-fe engine. Unfortunately within the past 5000 miles or so the car has started pinging when under load (ie going up a hill). The engine has 170,000 on it and according to the original owner, it has never been touched. Someone suggested give it high octane fuel, so I purchased octane booster which had no effect on the pinging issue, another person suggested I check the oil. It can't be the oil because I always make sure theres an ample amount of oil because it has a leak which I suspect is because of the valve cover gasket which brings me to my next suggestion, should i replace the valve cover gasket? Three of the four spark plugs have oil filling up in them (some varying worse than others). Is it possible that the oil in these cavities is fouling the spark plugs, causing detonation?
FYI - I don't think its carbon buildup either because the previous owner had the fuel injectors cleaned some 20000 miles ago.
Any thoughts appreciated, thanks in advanc.....
edit: *also, she runs a little rough when idling, not consistently. it'll run smooth and then it feels like its about to stall but catches itself.