Volvo: Volvo 1988 740 GLE with low city MPG and up for Emissions testing., warm ups, octane gas

Question
I tried the the key to light up things on the dash. There is  no check engine light. There is some squares that don't turn on. I am sort of starting to believe that there is no check engine light on this car.

I heard that there is an AirBox thermostat that controls the temperature of the Air that gets to the AMM. But I don't find it in my AirBox anywhere. At the JunkYard though, I did see it. Is my car missing it and that is what is scrowing it up or the car doesn't come with it?

Also, in my search after my question to you, I found people talking about cleaning the fuel injectors at a shop/dealer would help. Do you think this might help?

Also, some other talked about something called Cold Start valve. Where is that exactly and how can I know if it is faulty?

Thanks very much for your replies.


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-----Answer-----
Hameed,
It would seem that you have replaced all the parts that control the fuel system. Try changing driving habits, like 30 second warm ups and easy take off from stops, and give that higher octane gas a try.
If your AMM has 016 as the last three numbers in the Bosch numbers then you have a system that uses the check engine light and stores fault codes. Also most times if you turn on the key to light all the dash lights it should show up.
If there is a rubber plug on the front of the instrument cluster pull it out and push the service reset button. If no plug the button is on the rear of the cluster and you need to reach up from the bottom and go to about the 60 MPH area and there is a button that will reset the light.

Answer
Hameed,
Air box t/stat maybe, it is there for a reason and if it is always getting warmed air could maybe throw off the reading the control unit receives.
If the injectors need cleaning a shop with the right tools would be the best choice, so see if they will clean your injector and if that will help your mileage.
Cold start valves are mounted on the intake manifold. There is a fuel line going to it along with a electrical connection. Pull it out block the hole and see if it sprays fuel while the engine runs after it is warmed up.