My 86 4.3 engine runs fantastic... BUT when it is idleing, in drive or reverse, either cold or hot she is real noisy, like a loud fast ticking (almost a knocking). As soon as I accelerate it goes away. Idles great in park. Trouble codes all clean. If I force the idle higher and put it in drive it still does it until I accelerate.

I had an older Astro (TBI) which had noticeably loud injectors when everything else was quiet. I could hear it at idle in the vehicle with the windows shut.