Check Engine Idle
Start the car engine and let it run for two minutes so that the idle stabilizes. Now open the hood and unplug the connector from one of the injectors. Now see if the engine idle is worse or the same. If it is worse than this injector is dead. Repeat the same process with all the injectors inside your car.
Check Coil Resistance
Set your multi-meter to ohm settings. Now remove the electrical connector from one of the injectors. Attach the leads of multi-meter to the metal prangs of the injector. Take the reading.
Repeat the same for all the injectors.
If the reading of one of the injectors is too high or too low compared to the reading of the rest of the injectors, than it is faulty.
Use a flow meter to check the rate of flow of fuel to your engine.
If injectors are clogged than it will have lower flow rate. Cleaning it will improve the flow rate and performance of the engine.
See the Spray pattern
Open the hood and place a bright LED light over the spray pattern. Make sure that the spray pattern is regular. A poor spray pattern will indicate that your injectors are dirty and less fuel is entering your engine.
Check the injector tips
See if the fuel is leaking from the tip or it is clogged with dirt or carbon by simply rubbing your finger over it. It is one of the most effective methods to find the bad injectors.