Beezer

well here are the problems; ever since i bought the truck its always had a loud tapping but gets quieter as the engine gets hotter (exhaust leak maybe?) but the idle never got over 1000 rpm's even when cold but at normal operating temps is usually at around 750-800 is that normal? Now when i go to start it, it starts right up the rpm's jump to about 1000 then dips to about 400 and slowly climbs up to 800 but it feels kinda of rough i can feel the whole car shaking like if the ac was on. Just the other day coming home on the freeway the cel came on and off a couple of times for a few minutes at a time but now its gone is there any way i can check to see what the code was? The engine seems to be running fine i cant feel no power lost or anything but the idle's just got me a little concerned. Oh and when i drive it in 1st gear when revving up it sounds like water boiling but the noise gets lower as i go into the higher gears any ideas of what that could be? if anyone has any ideas or experience with any of these symptoms please shine some light on it. thanks

engine is a 22re manual