Without a picture I can’t help identify your insects. I can tell you that you are not the only one with this problem. All kinds of bugs, spiders and even mice find cars good places to hide out in the winter. The most common insects infesting cars are bed bugs, but they don’t fly so it can’t be those. There are pest control companies that can help but I think the recommendations from the following link give some good ideas to start with. Also you might try a sticky trap and send us a picture. Hope this helps. See: http://www.vulcantermite.com/education-and-prevention/remove-bugs-car/

These flying bugs are 1/16 of an inch or smaller in size. I have tried several sprays for insects, Diamateous Earth, Borax, Lysol and Nuvan strips. I have a son and these things are not good for him. They eggs still seem to keep hatching. I vacuum regularly and shampoo the inside. Nothing seems to stop them. I cannot get help from the exterminators in MN they do not treat cars. I dont even know if this species of bugs is known in Minnesota. They are very unusual. This is my last resort for help. If I use a sticky trap for these bugs I will not know if i have caught it due to the small size. They are mostly visible when flying around in the sunlight in the afternoon. Otherwise they are almost impossible to see. I think you would need a microscope and good lighting to see the sample. Do you have any other suggestions for these tiny bugs? Is there anyone else that can help me? I am running out of options.

I am wondering if you might have fruit flies. Try this. Get a jar lid and put some apple cider vinegar, water and a drop of Dawn dish soap. Set it on the dash board when the car is sitting around and see if you catch anything. Let me know if this works and I will continue to think about other options.

They are a lot smaller than fruit flies and faster. 

Without a clearer picture we can only guess what insect is involved. In order to get a better picture, take a piece of tape trapping the insect. If it is light colored tape it to a dark background, if dark colored tape it to a white background. Do this for at least three insects. The using a hand held magnifying glass, and a good light on the insect, take pictures with the insect magnified. We will then ask our entomologist for an identification. Hopefully we will be able to identify the insect and be able to suggest a solution.

After further consideration of your problem, here are some suggestions. You may be able to kill the insects by leaving your car in the sun all day with a window cracked. Temperatures may be high enough to kill the insects. Even if this kills the insects it may not get at the source of the problem. A thorough cleaning inside and out is necessary. Even a couple of Cherrios or a piece of candy can nourish insects for weeks and they may be hidden under or between the seats or even in car vents. Have your car dealer change the cabin air filter. Also have the engine compartment checked for signs of nests. They or you can wash the engine compartment down with cleaning supplies such as Simple Green which is nontoxic and biodegradable. Also have you purchased the car recently? New or used? If the car was in a flood, it may have harbored insects within the upholstery, doors etc. Do the insects bite? This answer could narrow the search considerably. How long have you noticed this problem? There are many small flying insects that hatch in the spring. All of the substances/chemicals you mentioned are used for crawling insects such as cockroaches; so I am not surprised that they did not work for these flying insects. You could also try insect repellants that are used for skin and clothing like picardin, permethrin or bimethrin on the seats and carpet..just be sure to air the car out during and after application. While they are safe for contact you do not want to inhale them. Good luck with this persistent problem.