Apparently someone before you was changing the plugs/wires and when putting the bolts back for the EGR pipe they probably dropped it and said the heck with it and left it with just the one bolt. One is 10mm and the other is an 8mm. A little tricky to get them both in and started, plus tightened down together to get a good tight fit into the back of the upper manifold with a thin blue gasket for a good seal.
Not sure what the symptoms would be because that pipe isn't tightened but it will cause a leak. I'd try and find a bolt that would fit and get it all tightened up.
