Got a good one for ya

I have a 1998 blazer 4.3 4wd. I repaced spider assembly but now I got a grinding noise at idle, idle is running 1200rpm if it trys to adjust down to 800 engine will make grinding noise then stall. Was not doing before I changed spider and when you rev it up there is no noise or if you put it under load. Its only present at idle and shutdown
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