I have a Carrier natural gas furnace. Model 58DHC075-HC
I think it is 92000 BTU. It was made aroung 1990
The furnace ignites OK, but then after a few seconds the flame foes out.
I guess this might be due to a faulty flame detector. Is there any way I can be sure of thuis befoire I order a fl;ame detorcor?
Is there any other possible cause I should check?

Carefully remove and clean metal rod on flame sensor with sand paper. Replace and try to fire it over.

Also see other problems with this unit.

https://www.askmehelpdesk.com/heating-air-conditioning/carrier-furnace-will-not-ignite-158980.html

This happened to me but on a more variable scale. Make sure that the outside exhaust is not blowing towards your intake. The oxygen-poor air was being sucked into the intake, and the flame "smothered" and fluttered-out. Re-aimed the exhaust, and has been perfect since.