Toyota Repair: 91 toyota four runner, toyota four runner, piston ring

Question
I just bought this and am having problems with it. It is idling eraticaly at times. It will run fine for about 5 minutes then start idling up and running rough. If I rev the motor it runs smooth again for a few minutes. Sometimes the idle will bounce from 1200 to 2000 rpms back and forth. I did a tune up on it new plugs, wires, rotor, and cap. Two plugs were fouled looked to a fuel problem. Any help would be great at this point.
Thanks Sam

Answer
I'm afraid I don't have a real good answer for you going by what you are telling me, there could be a lot of possible causes for this which probably why the previous owner sold it so it seems that you bought this 4-Runner that had some problems already.  The two spark plugs that were fouled would indicate a piston ring problem with those cylinders, I think it would be a good idea to have a repair shop do a compression test and a headgasket leak test on this engine because it seems that it has a serious problem.