88 Supra - Problem Holding Idle

[bills1988]

My 88 has 130K miles and recently began to drop idle speed "intermittently". Would usually start fine and the idle would drift down from about 1200 to the spec 800 (this is normal). It seems after driving and warming up to operating temp, and when I pull up to a stop light, the idle will sometimes (not always) drop to about 400-600 rpm. It usually recovers, but not always. Like I said, it is intermittent. The Toyota dealer/mechanic said it was probably the ISC Valve (Idle Speed Control Valve) which he called a Idle Stepper Motor. He said it may have some mechanical shaft wear causing the problem. This is an easy part to replace, but it is an expensive part (about $400+ online). I plan to continue monitoring it and seeing if I can live with it or at least determine the exact conditions when it happens. Here is the procedure (there are two pages, 106 & 107) for checking out the ISC:
http://www.cygnusx1.net/Supra/Librar...spx?S=FI&P=106

Hope this helps.