almost every time i cold start my car (which is a 1991 NX2000), it wont die, but it sounds/feels like it's going to. when i let it idle, it'll go from 800 RPM's, and dip repeatedly down to around 500. it definitely isn't supposed to do that. and once the car warms up it's fine. it idles around 800 RPM's like it's supposed to, and if i start it while the engine is warm, it's fine. any ideas what that could be? i'm thinking idle control valve or something to that effect, but i'm not so car savvy that i want to start my own diagnosing quite yet.