engine idle no oil pressure
 

i have a '96 chevy s10 blazer with the vortec 4.3, the intake manifold gaskets blew like all the bad plastic ones and it has been replaced with the new felpro ones. after this i started driving again and i noticed as the engine gets about 190 deg, the oil pressure drops down to the red line and the idiot light comes on at idle (500-600RPM). when driving it with the engine at about 1500RPM the oil stays at about 20psi. on start up the pressure is at just over 40psi. the engine does have a small tick that knocks at about 2300RPM, i have not determind if this is a lifter, crank bearring, or an injector that doesnt want to fire right. is there any way to adjust the oil pressure? let me know your thoughts. thanks, john

Is it throwing a code? Also your Crankshaft journal or rod bearings could be worn and the bearing clearance would be too high. And the knocking could be a lifter not getting enough oil for lubrication and etc.