sounds like carbon build up wich is common with todays crappy fuels and hard use of small engines..Its normal..If you bring each piston up to the top it can be cleaned off pretty easy with a scotch brite.The carbon is what can cause a engine to diesel when the idle is too high.The carbon will glow red and act as a ignition to left over fuel cause the diesel effect..Its not really too common on toyotas I have found but still worth cleaning off..Your compression sound like its good so throw your head on and call it good...
