well a 90 LS does not have a knock senser at all so you will not need it.The 94-up does but if its going in a 91 integra, then no plug on the 91 engine harnes will be there to plug in.there for no need for it....
as far as the idling problem ,check the codes from the ECU
& make sure the led is not blinking,hope that helps
if not contact me..
Scott