GM-GMC: low idle on 1993 Chevrolet Pickup truck 4x4, chevrolet pickup truck, air control valve

Question
I have a 1993 Chevrolet Pickup truck 4x4 with a 350 5.7 liter v8 engine. My question is my truck ever since Ive owned it idles to low it gets worse when the engine gets up to operating temperature it has even died a few timew because of the low idle and it has made the oil pressure also drop pretty low im not sure if this other part is related or not but also when I turn on my heater in my truck to defrost have it on high it makes the idle surge jumping back and forth. The idle on my truck when in drive is around 200 - 300 rpm which I know isnt right for an automatic transmission. I put in a new thermostat as well because it would get up to 210 degrees then drop down then it would start climbing back to 210 then drop and it would consistently do this and it seems to put out less heat then my other truck which is a 1989 chevrolet with a 305 5.0 liter im not sure this might have nothing to do with the idle at all but I thought id include it just in case.

Answer
There are a few things that you can check/try.  First things first, you should remove the idle air control valve and see if the port is restricted or block with carbon.  If you haven't already, cleaning the throttle body is always good maintenance. In order to see if the IAC is functioning properly you will need a scanner. You can also check the timing, timing can cause a low unsteady idle.  As a last resort there is a screw for setting the throttle position.  It is not recommended to use it for setting the idle but if all else fails, it may get you by in a pinch.  However, doing this usually compensates for something else that is malfunctioning.
Hope this helps