Hi, i am a newbie and could use some help! Idle is at 1200 rpm in park. In gear drops to 700 or 800 rpm and sometimes stalls. Car runs good until at operating temperature. Hesistates and misses slightly during acceleration at any speed. Code 12 (RPM) is the only code I have seen. I have cleaned the throttle body thoroughly. New distributor cap, rotor and wires. Fuel injectors are clicking. Any ideas appreciated!!!

I read Code 12 as "No rpm signal to ECM"

This is Crankshaft Position Sensor or distributor or their respective electrical circuits.

Check your ECT sensor. Engine Coolant Temperature sensor. That thing could be faulty, and maybe the ISC Valve, Idle Speed Control Valve.
I had a similar problem and replaced both parts to have it completely fixed.