1994 sentra xe with some major problems.help!!

ok well i'll start off saying i have a 1993 Se-r thjat gets bad gas mileage(around 12mpg)yes this is not joke!!! the engine runs great but the auto tranny slips. ok so i bought i 1994 xe and with the 5spd. well i found out that 5th is shot!!!!! argh!!! and one of the rear wheel studs is busted. but the engine is wanting to die!!! i'll let it warm up a little and it will idle fine, but if you rev it and then let off the gas it will some times stumble and or die(after it revs). it will go around a couple of blocks and then when you put it in neutral to come to a stop it will die. and its not losing vaccum from the brake booster, becuase it dies before you hit the brake. i checked the spark plugs and they were shot so i changed them. and i took the fuel filter off and blew it out and the gas was clean. but what could cause it to die like this? and how do you change the wheel studs? and is there any way to fix 5th gear at a decent cost? mabye setting the idle up? (but how do you do that?)

oh by the way the speedometer doesnt work either...

what's the mileage on your car(well, it might not be accurate since ur speed meter isn't working)
anyway, if it's really really high, then I don't think it's worth to fix those problems.

is the check engine light on?

about the idel, I guess it's the MAF sensor.
my car used to do exactly the same thing,
fixed it by replacing the $520 MAF sensor.
I believe that the MAF for 94 sentra is much cheaper

im before spending 100's of dollars on something that might fix my problem. i'm gonna try setting the idle up, because when the car is "cold" it will run and drive fine. but it seems to me that when the cold air idle shuts off it idles to low. and the 12 miles to the gallon is the 93 se-r not the 94 xe im talking about. im getting like 30+ miles to the gallon with the 94.... when i can keep it running. :screwy: but the check engine light was on and then i put a new muffler back on and it turned off. but last night it turned back on again. basically i need to know how to set the idle higher. and i also need to know how to take out a rear wheel stud to replace it. (one broke off) thanks in advance.

im before spending 100's of dollars on something that might fix my problem. i'm gonna try setting the idle up, because when the car is "cold" it will run and drive fine. but it seems to me that when the cold air idle shuts off it idles to low. and the 12 miles to the gallon is the 93 se-r not the 94 xe im talking about. im getting like 30+ miles to the gallon with the 94.... when i can keep it running. :screwy: but the check engine light was on and then i put a new muffler back on and it turned off. but last night it turned back on again. basically i need to know how to set the idle higher. and i also need to know how to take out a rear wheel stud to replace it. (one broke off) thanks in advance.

si si....exactly, gas mileage is pretty much the same, it's just the idle.
when it's cold, it's just fine.
when engine starts warm up, it might stall....anytime or when u let go of the gas.
3 shops told me to replace the idle controller.
I did, and it didn't help at all.
went back to the dealer, then they detected it's the MAF sensor.
try to get it fix asap, cause if the car doesn't get the fuel/air ratio
right, it might damage the cat converter.

well, at least I think that's why my cat went bad @ only 80k.....