Idle problem, Please HELP!!!!

[omegared19]

I have a 93 240sx hatch back with a red top sr20det from a 94 180sx. The only modifications I have made to the motor are a greddy oil pan and a koyo radiator. My issue is that at cold start the car does not idle at 1500 rpm's. It idles at about 900 to 1100. Also if I don't tap the throttle, it will start to drop rpm's and die. I also have a similar problem as far as putting the clutch in and the idle dropping to almost 300 rpm's then recovering. I replaced the IACV with a brand new one, but no luck. I also replaced the O2 sensor just in case. I couldn't find any vacuum leaks.....but then again I am probabally looking in the wrong place. PLEASE someone help.