For almost a year and a half my 2001 Tacoma 4x4 has been making pinging, knocking sounds, much like one would hear after getting bad gasoline. That might be what started this problem, who knows. For 4 years I used mid-grade gas. After the pinging started I went to premium which helped for awhile,then the pinging started back again. Over time it got so bad that any acceleration make the truck sound like the front end was loose and gonna fall out. It was very embarrassing too. About 4 months ago I went to a toyota service dept. who put in a 5 dollar can of top engine cleaner and charged me 75 dollars. It never helped a thing. Then a month later ,I went for my 120K service, thinking that getting plugs and other things changed would help. Nothing was helping and no one could tell me what was wrong. Then only 2 or 3 weeks after getting serviced, my engine light came on. Had the mass air flow sensor changed and the pinging and chattering has gone away. I've gone back to mid grade gas and everything is fine now. I just wanted to pass this along. If anyone wants to comment or add to this, I would like to read what you have to say.