You can run injector cleaner through it. If you are worried that they might be dirty, sending them away is your best option. Taking them out of a KL is not that hard. Two plugs, 4 bolts, just dont drop the plastic spacers underneath (4 black things, you will drop them ).
I sent mine away and got cleaned for $20 per injector but they replace all the O rings and put in new seals. Its a worth while investment on our old cars. Car will run smoother, better fuel economy and better for your engine. Changing fuel filter should be done at same time if you cant remember if its ever been done.