Toyota running rich
Do you have check lights on your dash?If so, have you checked for codes & usedthe internet to look them up?Check fuel pressure with a gaugeYou should have O2 Sensor Codes, if it runs richThe cause may not be the sensor that reports thecondition, unless they have not been changed at around 100,000 miles. They just report the converter gasesto the computerAny vacuum leaks anywhere,even in the exhaust systembefore the converter, will lean out the exhaust gases & thecomputer will in turn pulse the injectors longer & you get what you have.There are many causes that can take place,a looseair filter cover,something simple,a failed,dirty or stuckinjector.No --putting something in the gas tank at 12 oz to 15 gallonsof gas, is a waste of time & moneyYou really need the factory diagnostic manuals, soyou can follow charts etc to get to the issue.The Haynes books won't be of any valueIs the engine mechanically sound after 10 years or moreIt may be using oil & have issues you can't resolve?Did you buy it used? In that case your guaranteedthat the oil wasn't changed at 4,000 or less & the lifeof the engine reduced