okay so i was wondering why my step dads nissan hardbody breaths, it does it all the time, it will go from 1 to 2, sometimes 2.5 rpm's, its done it for ever since i could remember, and i know of 3 other trucks that do it, and its really bad on gas, hes got a 84 3.0 in it and its efi, manual tranny, 31's hes got a bad exhaust leak in between the bed of the truck to the point wen u start it on a cold morning it looks like its gone up in flames, and smoke barrels out from the crack between the bed and body, dont no if ne of this info will help but im guessing so, ne input is welcomed