I bought 86 IROC plugs were fouled check engine light on hard to start running rough, replaced plugs, wires, cap rotor, coil,and egr valveswapped intake fuel rail sensors off friends car still same problem, replaced coolant temp sensor and adjusted throttle position sensor run better but still hard to start rough idle while cold any ideas what else can cause symptoms

Code 15 is the ECT, engine coolant temp sensor. There are two temp sensors, une for the temp gauge, and one for the ECM. Make sure you changed the one used by the ECM.

replaced one on front of intake the sensor in block is missing aftermarket temp gauge in hole

where is the map sensor located found plug on passenger side not attached to a sensor is this the one for map sensor. will no map sensor cause this problem