engine pings on 1990 Toyota Pickup

My engine pings on light throttle loads. Not under heavy loads like full throttle. Timing is on etc. What could be wrong

2 answers
+1 on checking EGR. Pull the valve off, and check the small vacuum tube on the side of the EGR valve. It could be totally clogged up with gunk. If so, clean it out. Clean the rest of the inside of the valve as well, with carb cleaner.

Make sure the spark plugs aren't too old, as that can cause ping.

You can also try cleaning the combustion chamber deposits out, via fuel system cleaners. A good all-at-once cleaner to try is GM's Top Engine Clean.

Make sure vacuum lines are all good, especially to the EGR valve and the EGR vacuum regulator.

Make sure you have a stock or a 180 thermostat. Too cold or overheating can both end up causing ping.
check the egr system. that controls overheating in the cumbustion chamber which is the ping you here.

Roy