I have a 1991 Formula with a 350 engine and the engine has a rattle noise now, mainly when gas is given and shop checked all ac and found that black box behind ac compressor with the 2 plug ins bad, they said it was bad, can this be replaced by myself or a pro thing? Dont want to get ripped of, did any one have this problem, they said it was an emission problem, thanks! Andy

 

Off the top of my head I don't remember but, on a serpentine belt setup the compressor is on the pass side right ? If so the little black 'box' (has some hoses connected to it) is for the AIR diverer valves (emissions crap). The plugs go to the switching solonoids which switches weather the air from the pump goes to the manifolds or the converter. If you don't feel like fixing it, you can just unplug them with no ill effects or replace the solonoids if you really feel you want to.. it is an DIY type job though if you feel up to tackling it.
I've junked all that on both my cars because I don't have emission testing where I live.

 

Thanks a lot for the info! But what is the name of it and is that a dealer only part or any auto store? I want to get it right before car dies, it sounds terrible now like that. andy

 

The 'box' part is mainly for appearance only.. what is underneath the 'fascia' (box) is the AIR diverter valve solonoids. I doubt (but won't say you can't get them from an autopart store) you can get the solonoids from just anywhere but, really also, they don't make any noise aside from a brief clicking sound (like a relay). I'd guess any (constant) noise made would be from from the AIR pump itself. I question how much sense that made to you