if I add 24lbs to my 1994 Mustang GT
 

Do I have to have a new computer in it like a cobra, or a STAGE2 CHIP T4M0 J4J1? If your wondering. It's running like crap, can't keep an idle, back fires, runs rough. And I did alot, new IAC, new TPS, new tuneup, new PCV valve. All the works.

you cannot add 24# injectors without installing a calibrated maf, OR tuning the ECM

Right, so adding a STAGE2 CHIP T4M0 J4J1 will fix this right?

dude... T4MO and J4J1 are catch codes for the GT and Cobra manual ECM's...

before you buy ANYTHING please link me to what you are looking at so I can prevent you from making a typical noob mistake

How noble

its a common mistake to think you can make more power by adding larger injectors.
ill say what i know and give my opinion.
normally if a motor isnt built with better heads, came, intake and close to 300hp the injectors will not help but actually make things worse.the maf is reading for a air mixture with 19# injectors not 24# this causes problems right there.adding more fuel but the same amount of air doesnt create more power. there is a ideal air to fuel mix thats most effective. thats why people get things tuned.also im not sure but a adjustable fuel pressure regulator is usually needed too.if the stock heads are restricting you from flowing good enough or the stock intake is to restrictive then you will never need as much fuel as the 24# injectors flow without a adjustable fuel pressure regulator.
its said that the 19s will support up to 300hp after which 24 are needed.
if you insist on having 24lb injectors i suggest using a 93 cobra ecu and maf. but its a waste if you ask me and unlike a regular A9L maf ecu the 93 cobra is set for 24lb injectors and nothing else wheres the a9l is more flexible. and sadly a 93 cobra doesnt make nough power to need 24s! its rated at 245hp i think.
ADDERMK2 is a ASS but from what i see he is a nerd who knows alot more than most people on here except mjr46. either of these 2 people are good for advice.adder is not so nice with people who are new. mjr46 is alot more patient. i would read up and use the search feature and gather info and knowledge before buying any more parts. and please pu the stock injectors back in. and just a fyi im a redneck and not like on here so dont get to friendly with me if you dont want to be hated on here.
as to my sugestion. you need a intake, tb and differant maf that flows enough to justify the 24s. good luck

First you need to check for a vac leaks. Have you checked your timing?

^^ Sounds like someone is sucking up a little to not be on post approval ;)