fast idle

recently i replaced my alternator cause it was putting out less tha 12 volts. i spotted a leaky cooling hose so i drained the anitfreeze. put on the new alternator and plugged everything back in. now when i start the car it jumos to 3500 rpm. smooth but way to fast. no binding linkage, cleared the ecu. left the neg battery cable off for half hour. car will idle slow with evac unplugged but very rough. as soon as you plug in the evac the idle jumps up to 3500. any suggestions out there? thanks

does it only idle high when cold or all the time ?