91 sentra idle problems

well if ANYONE has ANY suggestions, please let me know. also, car has an aftermarket ractive tach installed from owner before me. the only problem with this is that it only works when you turn on the headlights.( hence he wired it to the dash lights or something,) anyway i dont care about the tach so much as it does not effect the performance of my car, i would however like it to start without assistance so PLEASE ANYBODY please help thank you

well i am bringing it in to the truck shop i work at tomorrow to change the oil. i know its not the air filter but will double check. the fuel filter looks like it was replaced,but whoever did it cut the hose or something because you can see this little plastic deal in between the now 2 sections of hose with a hose clamp that is way to big on either side...could be an issue of not enough fuel from there i guess, but why only affect at the start up of vehicle?

i clean the crap out of IACV still same. will idle at about 600 after warm up

hey yeah, well i bought the car with this condition. so to answer your question no maintenence had been done prior to this happening. i have put new air filter spark plugs oil etc. (routine) since who knows when the previous owner has done these things. anyway, i will have to try unhooking tach wires due to potential gremlins haha. but how would you test if the IACV is working? oh all hoses seem to be going where they should and doing what they should.
thanks

air intake system is stock, original. well yesterday my brakes went out. thank god for manual transmission. anyway took undercairage plastic protecter deal off( halfway down driver side of car beacuase that was where leaking brake fluid was coming from. there are 5 or six metal lines, couldnt tell which one was leaking so tried to take the clip holding all the lines together closest to the leak, screw head broke off (rust/wetness) took a screwdriver and hammer to try and quick rig a way to get screw out. wellflathead went through clip and hit what is apparently a fuel line. so now i have gas AND brake fluid dripping out of about the same spot. long story long, are those 5 lines =3 gas, and 2 brake? oh i guess having to step on the gas pedal to get my sentra to sstart wasnt so bad haha.....