Irregular engine idle (Miata 1.8L)

This is what I have a 97 Miata 1.8L 4 cyl M/T it has modified intake: cone filter and a u shaped computer that is definitely not stock.

-Well when I start the engine at cold the rpms jump up to 1750 rpm and then wind up to 2250 and back and back down again up and down
consistently
-As the engine worms up the revving stays in the same range but it gets faster. If I'm driving all day (hot engine) the engine fluxuautes really fast almost spazing.
-The irregular revving is strong enough to keep the car driving (it doasn't stall)when it's in gear and i take my foot off gast it will speed the car up to 2250 rpm and choke down to 1750 and continueusly faster, then slower, faster, then slower, it happened all of a sudden one day I cant explain it? I need help !!!!!