i got my 93 nissan sentra eccs and rpm always goes down... i replaced fuel injector,rattle valve,air flow sensor,even fuel pump, tension wire, spark plugs, capacitor which is my stupid mechanic advice. Eventhough i replaced all i mentioned still my engine wont run smooth and my rpm always goes down. My last option is airconditioning system, is it true that this 93 nissan sentra eccs wont run smoothly if no preon?????? i need your advice my bros and sis plssss....