The loop code needs an if else statement;
if ((sensorReading < threshold) && (sensorReading > sensorMin))
{
Serial.print("blowing ");
Serial.println(sensorReading);
digitalWrite (motorPin,HIGH);
}
else
{
Serial.print("Not blowing ");
Serial.println(sensorReading);
digitalWrite (motorPin, LOW);
}
That way the motor is on when the sensor is in range and off when its not. No delays