Hi Ed here:
FNG
On my 90 Si 1.6 Every second or third stop light when i'm sitting there the idle suddenly drops 150 Rpm or so, then slowly comes back up to spec. and stays there.It is indeed intermittent , at other times it just sits there and purrs like a cream fed ***** cat. EAVC?

 

do you mean IACV? (idle air control valve)
or do the older civics not have this?

 

Hi ed here
It's called a EACV which is wired to the 2 p connector
Ed.

 

well all i can say is do a throttle boby cleaning, clean IACV, too much carbon build up in IACV would cause your rpm to be lower than normal while idleing