94 Intrepid probs

94 intrepid radiator problems. Was bone dry on coolant, filled it with coolant (about 2 gallons, did not overfill). Let car run for about 15 minutes then the radiator reservoir started smoking/steaming, no odor or anything. No overheating lights came on in the dash. Car needs thermostat, isnt one currently installed. Reservoir was the only part smoking/steaming. Is this a major problem or is the smoke just excessive coolant being burned off around the reservoir cap? Please help!

Also, what would be the cause for it to idle roughly? Or is it just the fact it has 187000 miles on it...

Smoke or Steam coming out of the coolant reservoir is not a normal thing. You may have a bad head gasket, and that would explain why the coolant ran dry as the combustion pressure going through the cooling system pushed all the coolant out of the overflow. You might want to pull the dipstick and see if the oil is milky in appearance, if so your getting coolant in the oil too. Either way if the head gasket is toast that is why your loosing the coolant and most likely why the engine is running rough.

I agree with the head gasket syndrome. What engine is this? 3.5?