My dad has an 88 prelude S with dual carbs. It idles fine when it's cold but when it warms up completly it idles at about 800 rpm for about 30 secounds then drops and almost dies then goes back up to 800 rpm and then starts over agian.

 

uhmmm check for vacume leaks...check all the hoses....worn hoses etc..

 

those s' were known to have problems like that, make sure there are no vac leaks like semnos said and also check stupid stuff, like auto choke and that your air filter is clean etc... little stuff like that can wreak havoc on carbed cars like ludes and accords