SjCiViCHB

Well i need some help trying to fix my car before anything gets worst and i'm trying to get BAR'd and since i didn't get too much help from the EG forum, thought i would try here also...
Well here is my modifications...

93 Civic Dx w/ 94 B18C1 w/ Skunk2 intake manifold, ITR Throttle cable, and AEM Intake and then everything else is stock.

Well my problem is that when I cruise at say 70-80mph the car seems to stutter and feel like its having trouble staying at that speed and backfiring. Also when accelarting from 0mph sometimes the rpm gets stuck around 3-4.5K and backfires like crazy, but as soon as i let off the gas and put it in neutral and try again its fine. And my last problem is sometimes my idle fluxates, it would go from 1000-1500, sometimes up to 2000rpms. I changed the spark plugs, no help. Re-did my ignition timing, and problem still occurs. Also i checked all my vacumm lines and everything is intact and not leaking. I also tried looking fixing the FIT valve but I have no idea where thats at, I cant find it under my throttle body. I dont know what else to do, can anyone else help me and give me some ideas on what to check and hopefully fix this problem? Thanks in advance. Sorry if I didnt state my issue very clear, but I will do my best to answer anyone's question to help me fix this problem. Thanks again.