Rough idle on an 88 LX

Ever since I bought my 88 LX, it has idled excessively rough. Not a misfire, it idles like a tractor. I know 2.3L's are not known for smooth operation, but this is definitly worse than normal. Here is what I have done so far to try and correct the issue: New plugs (Autolite copper), wires, cap, rotor, oil change, intake cleaning, new air filter, ran 3 tanks of fuel injector cleaner, installed new vacuum lines to replace damaged ones, replaced EGR valve, removed and cleaned idle air controller, and had a new oxygen sensor installed. The computer throws no codes when KOER, KOEO, and CM codes are retrieved. It is bone stock with 74K miles. The previous owner told me that the car has always had synthetic oil since new (I am continuing to use 10W30 Mobil 1 or 5W40 Rotella Synthetic) and it shows. It does not have any leaks and burns very little oil. My only concern is the fact that synthetic oil is molecularily very thin. Often times when I start the car, the oil pressure gauge reads 50psi (I know they can be innacurate) but after the engine is warm, it will drop to 15-30psi (15 at idle, 30 under accleration). My fear is that the cam is worn down and causing this, but, above idle, it does run very well and deliver good fuel economy. So I guess my question is 2 part: What on earth could be causing my low, rough idle (sometimes stalls when going from drive into park) and would synthetic oil really cause low oil pressure and excessive engine wear?
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Check IAC valve. Valve on side of throttle body maybe sturck or dirty and needs cleaning. Oil pressures seems low but I have turbo motor don't know if differant someone else will have to help on that one.
I had disassembled and cleaned the IAC a few months ago, but I am beginning to wonder if it is failing. The oil pressure concerns me, but I don't know if it is the gauge or not and I don't have a way of checking the real oil pressure.