I have a 89 Honda Civic, and the check engine light comes on.When the light comes on the car feels like it gears down, and when the light goes off, the engine takes off like normal. I'm thinking that it's a sensor,but can't figure out which one. The plugs and wires need to be changed, and I have a leak in my exhaust too. I'm figuring it's one of these sensors. Can you tell me how to try to find out if this is the problem, before I take it to a shop?

Check for any diagnostic trouble codes. It wouldn't surprise me if your oxygen sensor is bad.

Try this link it fixed my car easy as pie...
https://www.askmehelpdesk.com/cars-trucks/faq-honda-civic-wont-start-read-here-before-you-post-9924.html

After soldering the main relay it started up and has been running great ever since.