I have a 1997 Corolla with 155,000 miles that recently started pinging and also knocking during driving in town. Using mid grade gasoline reduced the pinging and knocking but only high test would almost eliminate it. The car idles normally, drives well on the highway, gets 30-33 mpg at speeds of 75 mph and the water temperature is normal. Most of my driving has been on the highway and there is still some very slight pinging when the engine is cold which suggests that carbon deposits are not the cause. An OBD analyzer does not show any codes. What is the most likely cause for this problem?
I’d say that your plugs are wrong (too hot) or the ignition timing is overadvanced. Have the timing checked and verify that the spark plugs are correct and correctly gapped.
My first guess would be an EGR system fault, considering the vehicle has 155k miles on it. Sticking pintle, clogged passages, etc. - OBD codes or not.
Too much timing advance can also cause it but this should not be a factor unless the timing belt and/or distributor has been dinked around with.
Had any timing belt work done lately?
The spark plugs were changed at 100k and they are correct. The timming belt was also changed at 100k. There is no adjustment capability with the distributor.