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Re: '93 900S Idle Speed Posted by JimBlake [Email] (#141) [Profile/Gallery] (more from JimBlake) on Wed, 18 May 2005 07:18:08 In Reply to: Re: '93 900S Idle Speed, Bernardi, Tue, 17 May 2005 20:17:25 Members do not see ads below this line. - Help Keep This Site Online - Signup |
My guess is the ECU is trying to drop the idle speed but can't because of extra air coming in beyond it's control. It uses the control range of the AICV, but it can't do more than close it.
If the throttle plate won't close against the throttlebody bore (dirt or mis-adjustment?), that's one source of excess air. If the AICV doesn't operate smoothly, that's just sloppy control action. Vacuum leaks are not only extra air, but it's also NOT measured by the air mass-flow meter.
There's also some conditions that put the system into a high-idle limp-home mode, for example a bad airflow meter. These would ALSO set off your check-engine light.
But the high-idle part of that is accomplished by shutting off the AICV & letting the rotor turn all the way to where it's open on the backside. Hard to explain, but if you look inside the AICV you'll notice when it springs 'closed' it's really open about 1/8" on the wrong side of the shutter. If the AICV electrical connection is flaky, it swings all the way over where it's opening again.
Strangely, if the physical idle stop screw or cable holds the throttle open, then the ECU tries to compensate by closing the IACV too far. When it does, the backside of the IACV opens up, increasing the idle.
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