If everything checks out, you may have to adjust the air bleed screw to bump up the idle. The screw is located on the top of the intake, towards the back. It is supposed to be covered by a black rubber plug, but sometimes it is missing. Turn it about half a turn clockwise (I think that is the right way), wait 15-30 seconds and see if the idle comes up and stabilizes. Keep adjusting it until you can get the hot idle to stabilize at 800RPM with all the accessories off (lights, heater blower, radio, ac, etc.).