My engine (1985 190e 2.3L 8V) pings under any load (taking off from a stop sign even). I know that it can be related to timing or crappy gas. I have filled the car with Hi-test and addded 2 cans of techron (to clean things out). I have also checked the timing and it is correct (vacuum advance apears to be functioning fine). Any suggestions? Do I add octane booster?