thats a dead hole...nothing to worry about..there is usually a roll pin in there blocking the air/fuel adjustment screw..that is the lower hole..most people (idk why,.. it drives me nuts!!!) pull the pin thinking they can magically make their truck run better by adjusting the A/F ...but alot of the time they dont pull the pin right and break off the ear..it won't hurt your truck....the only thing you should worry about is if someone messed up the adjustment for the air/fuel...