engine codes on 1992 Chevrolet Lumina APV

i just purchased this van and so far i have put a TPS and Cooling sensor on it, and it has a rough idle and the check engine light blinks on and off, and shows a code 15, any ideas?

Asked by for the 1992 Chevrolet Lumina APV
How is the engine temperature, is is normal? How about the wiring and the connector at the temperature sensor? Are you sure there is only the 15 code?

DTC - 15 Engine coolant temp sensor error (low temp indicated)