Bad idle, multiple probs???

[240sx88]

b4 any one bites my head off let me tell u i did search, any ways, my car idles rough, and shakes real bad in i give it gas. I think its my AIV valve, i know for a fact it is broken, but my problem is this, i have a lot fo back pressure too. tonight when i took it for a drive it drove great no back pressure no bad idle or ne thing. but idk if my aiv is the only problem im goin to replace it tom but if there is any idea's abot the backpressure would be great help. Oh by the way, its a 1990 240sx ka24e