simple electrical question
06-14-2009, 10:00 AM
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ATGATT
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simple electrical question
My car has an idle control valve that closes whenever the idle control unit (a circuit board) sends the signal to give it 12 volts. I want to yank out my idle control unit and just put a switch in the car to act as an on/off switch. How would I do this? The idle control valve just has two prongs on it. I don't really know anything about electronics other than how to solder.
06-14-2009, 01:08 PM
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Re: simple electrical question
Ok, so most cars don't use just a 12V signal to the idle control valve, because then you'd just have a valve that was all the way open or all the way closed. Most cars use a PWM (pulse width modulation) signal that is a square wave with with a variable high/low time. Some use a fixed frequency, some use a variable frequency. Not really important.
Anyway, what happens is that the PWM signal sent to the IACV coil is turned into an average current (by the coil's inductance), and that is what makes the IACV work in it's linear range instead of just all the way open and all the way closed. If you just give it a 12V signal, it will open all the way and if you don't give it a signal it will remain closed (obviously). So if you hook a switch up to it, you can have fully open or fully closed. As far as I can figure, that won't do very much in the way of idle control.
This, I'm assuming, is why there is an idle control unit on your car.
Anyway, what happens is that the PWM signal sent to the IACV coil is turned into an average current (by the coil's inductance), and that is what makes the IACV work in it's linear range instead of just all the way open and all the way closed. If you just give it a 12V signal, it will open all the way and if you don't give it a signal it will remain closed (obviously). So if you hook a switch up to it, you can have fully open or fully closed. As far as I can figure, that won't do very much in the way of idle control.
This, I'm assuming, is why there is an idle control unit on your car.
06-14-2009, 02:07 PM
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Re: simple electrical question
Yeah. This is 1985 mechanical injection baby (this injection system went into use in 1977 and the basic design of the injection system is from 1967). It's just an on/off valve, either all the way open or all the way closed. All the idle control unit does on this car is it takes info from the water and oil temp sensors to decide when to apply 12V (well, it also gets a signal from the oil pressure sensor and if the oil pressure drops too low it will open the valve then even if the engine is at operating temp). All the idle air goes through a bypass hose when the engine is hot, hence the full open/full closed operation.
Last edited by marlinspike; 06-14-2009 at 02:12 PM.
06-14-2009, 04:25 PM
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Re: simple electrical question
Ok, well if it's just a 12V signal, and some unknown current (which may be more than you want to put through a switch) you could probably just use a relay and a switch and be done with it. You might be able to just use a switch if the current is low enough, but you'll have to find that out with a multimeter.
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