[84LX89GT]

you don't have 90 horsepower....you have 88 Only one word comes to mind: TURBO! Thunderbird Turbo coupes came with the 2.3L and turbo and it's a fairly straight forward swap, you don't need to change much at all and you get about 140/150 horsepower. Add an intercooler and you'll be close to 180/190 horsepower. This is with close to only 6 lbs boost (i think that's what they have stock). The 1986 Mustang SVO had a turbo 2.3L with an intercooler and single to dual exhaust with chrome tips (stock) and made 200 horsepower and handled like crazy. If you can find a Mustang SVO you can swap that stuff over as well, but those cars are hard to find. Many people have adapted those engines to make over 400 horsepower, so you can make power with those. It's not really worth your time to spend too much money making it fast, when it would cost ALOT less to eventually upgrade to a 5.0L LX or GT or even transplant a 5.0L into your car (or whatever engine you want).

Cheap stuff:
take the big plastic piece that says FORD with a circle around it on the intake tract between the mass air flow sensor and throttle body and look inside. Notice how it goes from 2" in diameter to 1.5" in diameter. Take a sharp object like a box cutting knife (exacto knife) or razor blade and cut that restriction out. All that is, is an intake muffler.
Another thing that is restrictive and causes turbulance in the incoming air is the stock air box. You can buy a cone filter to replace the box, or you can adapt a 5.0L system to pull air in from the fenderwell (the stock 5.0L air box isn't bad at all). The 5.0L air box has a rubber hose connecting to the Mass air flow sensor that is easily adjustable to different sizes especially with the clips that come on them so i believe you can use the stock hardware. If nothing else, it's worth a try. You could also probably pick a stock airbox off of some one from this site for REAL CHEAP.

Good luck,