Agreed on old injectors that have been laying around, be cautious. I was lucky I had a friend that worked at Siemens, so I could give him my injectors for cleaning them and flowtesting. Saved me a lot of headaches. In a pinch, I've taken them off the car, removed the rubber o-rings, and soaked them in Seafoam for a bit. Seemed to help when I did that, I think I had an old injectors with the gas turning to varnish and clogged the injector.

Or just run Seafoam through it while it's still in the car. I seafoamed the car through the intake a few weeks ago to just run some cleaner through. I was impressed it corrected a someone off-kilter idle, so I guess it was in need of cleaning.

 

I normally dump in a whole bottle of SeaFoam (into the gas tank) every oil change. It helps.