MQ-9 gas sensor strange results

I'm trying to get the carbon monoxide level in room with MQ-9 sensor but the results are strange. When I power up first start increases result to some random point and than starts decreasing. If I change the sensor is the same problem.

I'm using this sensor: http://www.ebay.com/itm/1-PCS-New-MQ-9-Carbon-Monoxide-CO-Alarm-Combustible-Gas-Sensor-Module-/271634561006?pt=LH_DefaultDomain_0&hash=item3f3eae77ee

void setup() {
  Serial.begin(9600);
}

void loop() {
  float vol;
  int sensorValue = analogRead(A0);
  vol=(float)sensorValue;
  Serial.print("");
  Serial.println(vol);
  delay(100);
}

Sensor I hook up with +5V, gnd and A0. Sensor have 4 pins, the forth pin is D0 (digital output) but i didn't know how to use it. I was searching, but I only find examples with sensor that have 3 pins . should I use D0? how?

Thanks in advance and sorry for my english.

Did you read the datasheet that it needs 5V and 1.5V ? I suppose your module only sets it at 5V.

This page has some basic information : http://playground.arduino.cc/Main/MQGasSensors

D0 is the digital output, you can turn the potentionmeter for the comparator that makes D0 high at a certain level. Is the other pin an analog output ?

Yes I read it, but still don't know how to do it, it have 4 pins. +5V, GND, A0 (analog output), D0 (digital output), where can I connect 1.5V?

How do you meanto do it with this potentiometer and comparator? Yes it's analog output.

Use the AO, the analog output. After power up, let the heater heat the sensor for a few minutes. Are the values okay after 5 minutes ?

Did you do the pre-heat time ? You have to keep it turned on for 48 hours. Only after that it gives useable values.

I think the heater at 1.5V is not possible with that module.

The comparator is the black chip on the module. It uses the analog value and the potentiometer as inputs. It makes the DO high when the sensor value if above the potentiometer value.

After a few minutes the values on the two sensors were okay, except on the one where the sensor was totally missed(bad sensor).

No I haven't done a pre-heat time and adjustment. Is too late now?

I made a little research on this comparator but I haven't found anything usefull for my case. Can you please tell me a little more on how I can use it in my case or I do i even need it now when the values are okay?

any one?

i have exactly the same problem with mq-9. now if D0 should be connected then to which pin. ALR or HSW?

Real all of this. http://forum.arduino.cc/index.php?topic=208258.msg2575049#msg2575049post