Since the battery light was on, that will throw off a code in the ECU. You peel back the front passenger carpet, and turn the ignition on (no crank). Count the number of blinks of the light. Do this several times to confirm. It may throw off more than one code with blank interval in-between. number 1 code is elusive because it will do that just for turning the key on, so it might apply, it might not. There are references online for how to read the codes on 88-91 civics, or in a Haynes manual of the period. Could be alternator, how many miles on it? My guess is you have a #14 code for the idle air control valve, since you say you have some reason to believe it's 'going'. I had to clean my IACV (flip upside down, soak interior 30+ mins in throttle body cleaner - twice, rinse a little, probe with mini brush/pipe cleaner, screen should be clean and bright. If you get particles out of it, THAT is progress!). After reinstall you will get idle surge up and down once it's warmed up because of air bubbles in the cooling system. You have to burp when cold by squeezing upper and lower hose with rad cap off - several sessions of this - took me weeks. Also may be relevant: I also cleaned my fuel injectors the previous year. Particles can get in there too. And to be complete, first check the throttle body and clean that. I had goo on the edge of the plate that flaps up and down. That made it sticky here or there. Ask me questions I've been all through this the last 2 years.