I have a LS/vtec in my 98 hb.just put it in last weekend,so everything is NEW.when turn the car on it idles fine and with no problem at all,runs strong.but when I'm driving at around 3K rpms n I throw it neutral to slow down for a the traffic light or something the rpms drop real LOW n sometimes it stalls.I've checked everything that I think can cause it ,but its still doing it.the car idles at 800rpms,fuel pressure is set at 38psi.if that helps.any input would appreciated.thanks

 

make sure the ground to the thermostat housing is tightened.