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700 Series TBI

The TBI used for 87-88 Fiero 4 cylinder motors is the 700 series unit presently manufactured by Delphi Automotive for GM.
You can find Delphi’s public relations info for the 700 TBI here. The information includes images and general specification data. The articles that we’re interested in at the moment are “Throttle Bodies - Single Point” and “Throttle Bodies - Multec BottomFeed.” The first is the TBI unit and the second is the injector in more detail. Fiero uses the low-pressure version. (Note: Delphi changes things fairly regularly. If they still exist, these documents may be hard to find. I can't post them due to copyright.)
Below you can see how the TBI is setup and where some of it's components are. I also noted the MAT sensor for you. (MAT is also covered in theDIS article.)
• FPR, Fuel Pressure Regulator
• TPS, Throttle Position Sensor
• IAC, Idle Air Control motor
• F In/Out, Fuel Lines
• MAT, Manifold Air Temperature
The design of this TBI is really something. It can tolerate amazing amounts of crap in the fuel system without plugging the injector. There are screens right on the injector. You’d have to cover them nearlycompletely to block off injector flow. To get that much trash to the TBI, both the main filter and the pickup sock in the tank would have to fail or you’d have to have major corrosion damage to the inside of the fuel lines.
The 700 TBI is comprised of two modules. The upper section handles all the fuel metering and is the same regardless of what lower section is used. The lower section handles allthe air metering and contains the throttle plate and IAC. There is no fuel flow between the modules except what flows from the injector tip. 700 TBI bore diameter is determined entirely in the lower section. (If you were punching out a 700, you would only machine the lower half. The lower section, assuming there is enough metal, can be punched to the maximum diameter of the upper half.)
BTW, theTBI used for 87 and 88 Fiero L4 has a 45mm diameter main bore. The largest Delphi makes is 48mm. You could install a 48mm one but you'll need to ream the manifold and you probably won't gain much power.

Do I need to use injector cleaner in my gas?

Probably not. The cleaners already present in most pump gas should be more than enough. Keep in mind that this injector is not being heat soakedlike port injectors are after engine shutdown. It’s far from the intake valves and upstream of the throttle as well. That prevents fuel residue from cooking onto the injector.
The only time I can think of where cleaner might help is if the car sat parked for a long time. That should help wash away anything caused by stale fuel.
With this system, if you are finding allot of carbon in the TBI andintake then you have problems developing that need more than some cleaner. (You will likely also need to check/replace the MAT sensor.)

Throttle Position Sensor

The TPS is not adjustable. The ECM is programmed to accept any slight variation in the home position of the sensor and recalibrates the home position each time the engine is started.
The TPS does wear over time, but it should last manyyears under most conditions.
Do not attempt to clean the sensor and never spray it with solvents or pressure washers.
The easiest way to test the TPS is to use a sewing needle to probe the terminals. It’s long and very thin so you are less likely to cause a short if you slip. Simply slip the needle between the wire and the seal. If you short the terminals to anything you could fry the ECM!
Oneterminal will show 5V. Another terminal is ground. The last is the output. The TPS output should show less than 1.25 volt when the TBI is at idle. Output voltage should increase smoothly between idle and WOT. (Note: It is usually easier to test the sensor with an analog meter. Digital displays are often too jittery.)

The Injector

Note: Don't rely on the visual appearance of the injector...