1980 300 SD---Injector knock (sounds like a rod) -using a stethoscope, I determined that #5 injector had slap or knock so I ordered a replacement from the parts dept..

After replacing the injector I still have an even louder knock at idle. It does smooth out at about 1800 RPM. Valves are in spec.

Is the new injector at fault? Please advise. Thanks, Nate