The ISV in my 1990 doesn't hum at all. It is a tuneless, joyless accessory.
I suppose that leaves the ISCU at fault or a break in the wiring from the
ISCU to the ISV.

On Sun, Jan 24, 2010 at 1:51 PM, mark drillock <mdrillock@cox.net> wrote:

> Not so fast. The idle valve behavior depends on the version of the FI
> wiring harness. Lots of later vans power it from the fuel pump relay and
> so on those vans it WON'T hum with just the key on, the engine needs to
> be running for it to continuously hum.
>
> Years 86/87 power it from the ECU relay and on those vans it should hum
> whenever the key is on, engine running or not.
>
> Mark
>
>
> John Bange wrote:
>
>> .............
>>
>>
>> If the ISV isn't "humming" with the key at ON and the engine not running,
>> something in the idle control system isn't working. The valve is
>> controlled
>> via pulse width modulation, so when it's doing its job, it'll be
>> vibrating.
>> It's unfortunately not all that uncommon for the controller to crap out.
>> Still, I'd check all the wires first, make sure the controller is getting
>> 12v, it knows the throttle position switch is closing, and its connection
>> to
>> the valve is OK before buying another controller.
>>
>> --
>> John Bange
>>
>>

--
mordo
1990 Carat