Zerosheaven

yesterday i noticed while in first gear if i gun it and the RPMs reach around 3000 or so, then i need to make a sudden stop, when i push down the clutch and push the brake, the RPMs will drop down to 500 or so and it will seem like the car wants to idle, but then it will bounce right back up and everthing will seem normal,it seems to engage into gear fine and accelerate ok. my car is pretty much stock except for the free mods. i was thinking it may have somethign to do with my spark plugs w/ wires or maybe my air filter is old n dirty or something, what do you think??