WRX SCOOBY

hi iv a 94 wrx and its a bitlumpy ticking over only no and again and when i hold a 3ooo rpm the car is moveing back and forward very very slightly but if i gun it its fine its getting so annoying i want to sell it as i tryed so meny things to fix it im only just gone 21 so its hard enough to keep and mod and trying to sort this out and keep coming to dead ends
addice realy appriceated
thanks
i tryed these things
1.new plugs
2.new coyels
3.cleand piper x air filter
3.new maf
4.put old air box back in
5.cleaned solianied
6.tightend all pipes
its only done this sine i got a new block put in as i melted the last ones piston