Hi! I have a Automatic 98 Honda Civic and lately I've been having this problem where my car idles down to about 300 rmp when i stop. I'm worried because when I put my foot on the gas to go it stalls or vibrates weird like it's about to cut off. My brother says it may be my idle air control valve, but I'd like to get other suggestions without paying $64 for a diagnostics test.

Thanks!