1990 240sx idle defects

[mick]

I have been doing everything I can to smooth out the idle. Cleaned the IACV, TPS, MAF. Changed all vacuum lines and the O2 sensor. New plug wires. New coolant temp sensor. I adjusted the TPS and the Idle screw. I removed the AIV.

My idle is about 900rpm usually but on deceleration it drops to 500rpm then after 10 seconds of sitting at a red light it comes back up to 900rpm. I set it to 900rpm so it won't die at the red lights.The idle does a sudden drop as soon as I take my foot off the gas pedal.I haven't found a vacuum leak... My vacuum is 21 usually and drops to maybe 19 on deceleration.

The other thing is I have no fast idle. I have read every idle thread and I think I've tried everything.