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CruiseControl CruiseControl is offline
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Join Date: Mar 2005
Location: Australia
Posts: 145
Isn't the tachometer driven from the "brain"? This be the case, if there was a faulty sensor giving higher than actual RPM this would display a high tacho reading.

The following is assuming that this idle valve is a three wire two coil unit.
My understanding of the operation of the idle control valve is a "Push/Pull" PWM (Pulse Width Modulated) control operating the two internal coils at a fixed frequency (say 200Hz). Both coils are being driven with the time on for each coil changing (the PWM signal). That is say to hold the valve at a 40% open position the open coil is energised for about 40% duration and the close coil energised for about 60% of the duration (these percentages will change subject to the work load of the internal arnature). Hence if there is a problem with the circuit to the open coil the 60% duration of the close coil will drive the valve shut. - this aligns with your discription above of the valve slamming shut.
My knowlegde of idle valve control improved when getting the MoTeC ECU to drive the 3.2L idle valve, which after understanding both pieces of equipment now works a treat.
This PWM driver principal we also use on industrial actuators operating at 20kHz, and vary the time on/off for each direction.
Get that multimeter (or scope) and check the two output signals from the ECU at the valve plug. The fluke should have a % duration selection, use it. Don't bother with volts reading. I would be interested as to the operating frequency of the valve while you are there with the meter.


Last edited by CruiseControl; 11-28-2007 at 03:02 AM..
Old 11-28-2007, 02:40 AM
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