OK, today I decided to clean out the egr passages due to loss of power when accelerating. Whilst doing the removal of the fuel injectors one came out of the fuel rail and a small tiny part dropped out of the top of it, (it dropped out of end of the fuel injector that connects to the rail it looked kind of like a plunger of some sort) anyway this dropped out and was lose. I put everything back together, I am curious if anyone knows what this part might be and how serious it is that it is missing from one of the fuel injectors. Everything seems to be working fine and i plan on buying a new injector to replace it but for the time being is it ok to drive it?

Thanks