Miata Mailing List: October 1993, Message #210
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   From: Mike Rother 
Subject: Re:  Idle Problem
   Date: Thu, 21 Oct 1993 14:34:18 -0400

	From: Bill Kim 
	Subject: Idle Problem
	
	The description of the problem is as follows. When the rev's
	come down to idle it goes to about 200rpms and the car almost
	dies and then it comes back up and idles just fine.

This is a fairly common Miata problem;  often written up in Miata
magazine.  There seem to be a few different causes for the problem.
Mine went away when I "exercised" my Idle-Speed-Control Valve (ISC
Valve).  As a test for the ISC, the shop manual recommends
disconnecting it at idle, which moves its internal piston and raises
idle speed.  When I reconnected the ISC valve, my idle problem
disappeared.  Apparently, in my case, the ISC's piston was sticking in
its travel, causing a temporary drop in idle speed on deceleration -
until the piston finally moved and let bypass air through.