Setting idle on 2001 blazer

Should idle between 500-600. Clean your throttle body with the battery disconnected to help with the fluctuation. The roaring very well could be your fan clutch. Fan clutches are a known problem with our platform. If engaged, will sound like an airplane.

the idle is controlled by the computer and the idle speed motor if the idle is too low the first thing you should do is check for a vacume leak as this will directly effect the idle or revs as you say

try spraying the inside of throttle body with motor off with carb cleaner or starter fluid do not open and close throttle body while spraying but leave closed and blow it out with air should start idling at about 8.5 rpms

600 RPMS IN PARK

You probably have air between the master cylinder and the abs pump. Fill the reservior and have someone pump the brake and bleed the primary lines at the abs pump. Good luck.

could be numerous reasons. this is your best bet take it in to a mechanic and have your engine codes scanned. it is a minimal charge, some even do it for nothing it only takes 10 minutes.this will point you in the right direction.

Disconnect one wire connector at distributor and set at 10 degree's.

you might have a bad fuel pump just fought this problem on a frends car car start ok cold and hard starting after driving after a complete tune up the problem still exsisted replace the pump no more problems car cept setting an o2 senser code

Definitely engine mounts.