Scan the ECM? Does ECM match the tach? Note that Idle speed w/ scan tool active should be ~1000rpm.
Carefully pinch vac line to brake booster?
Line to booster or booster itself can be a vac leak issue.
Small changes of idle stop then IAC will adjust accordingly.
Too must and ECM can set DTC and/or engine could be hard to start.
reset the stop, See my Cave, Idle Stop
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)