Dlero

Hello everyone im new to the forum and this is my first post. I'm hoping to get some help with a problem im having on my xj. I have an 87 with the renix 4.0. I went to start the car today and it was running poorly and making a loud popping sound which sounding like it was coming from the intake manifold. The noise was really loud if you popped off intake tube. I took off the valve cover and this is the first thing I see:





I'm guessing that rod could be my problem. So I have a few questions. What exactly is it? It opens the exhaust valve doesnt it? Could it have caused other damage from coming loose? Can I just put it back under that cup thing and torque it down and be on my merry way? What would have caused it to come out in the first place?