ka24de running lean

alright my 93 s13 is running realling lean, ive gotten a new fuel filter in it, ive changed plug wires and plugs, gapped them,. it seems to be missing at idle, and if i put the clutch in while braking the car drops down to 300 rpm,then jumps back up,
what places should i really start to check to solve my problem

This could be a few things; I would do a check on your fuel pressure. But before that I would do the simple things such as making sure your piping to you throttle body after your Maf, is all air tight. Maybe even clean your IAC valve, the proper way is pretty hard to do on a ka but maybe the ghetto throttle body spray in the body may help, or narrow the problem to see what direction to lean towards. There will need to be a little more info for a better diagnostic.