1993 Chrysler Le Baron A few problems

Here is a brief history. I bought this car for $125.00. It needed a timing belt and a few body related items. Got the timing belt installed, and she fired right up. I have been driving the car for a bit.

I notice that at a stop the idle will usually sit at about 500 RPM, but somtimes itll go down as low as like 250. The engine doesnt stall and the check engine or check gauges light never comes on. But the car does run a bit rougher. Could my problem be a weak coil? I have adjusted the timing and no change.

Also, the oil pressure when you first start the car is about where it should be, but as the car warms up the oil pressure goes down to the last line on the 1/4 point instead of being at 3/4 when you first start it. If you get on the freeway with it itll gradually get higher, but the moment you take the exit ramp, its back down to 1/4 or just below. Bad gauge or sending unit? It may leak or burn a little bit of oil.

Also my cooing system: I am not sure exactly what is going on with this. It stays at the bottom line and when it heats up to the 1/4 point I see steam coming out the hood. The gauge willl go farther up if you dont turn the heater on. And the heat isnt always that hot. I was thinking water pump (heater core isnt the problem) but if you jam on the gas and get the motor up in RPMs it should lower the temp. I waited until the car was cool and opened the radiator. It appears that its just water in the system. Could that be my problem?