'88 5KSQ High Idle

[Marc Swanson]

> What's the "frequency valve"?

It controls the operation of the fuel metering head.  It is a ls a small
semi-cylindrical looking thing that is mounted near the flow plate.  On my 87
5ktq parts car it had a 2 pin green connector on it.  You can usually hear it
buzzing away with the car idling.

> The ISV?

Idle Stabilizer Valve.

> I jumpered a ground to the ISV body.
> No help.
>
> Now I'm looking into the temp sensors.  I see 2 temperature sensors at the
> outlet (inlet) on the block where the thermostat resides.  The 4 pronged
> multifunction one and another 2 pin one.  But the 2 pin one doesn't look
> like the one in the Bentley.  So I'm wondering if there is another one.

there is another one mounted to the head.  A single pin connector that looks
like a brass nail was driven into a sensor base.  There are two just like
that sensor.  One mounted in the head and one on the coolant flange.


> I believe here is one on the radiator.  What does that one do?

controls the radiator fan.

> I also thought the function of the 4 pronged one was the temperature gauge
> and the fuel management system (CIS-E III).

also air conditioning

> And that the function of the 2
> pinned one was for the Autocheck system.  So that leads me to believe that
> the multifunction one is bad.  I

Does your coolant gauge work?  If so, leave it alone.  The single pin sensor
is where you should focus your attention.... the one on the head is the one
that is supposed to be used by the ISV but sometimes the wires get mixed up
(it doesn't matter much) and the sensor it uses will be switched with the one
that the ECU uses on the coolant flange.

>  go through one of them per year, and this
> one is overdue.  Unfortunately, it is a $50 part.

the multifunction sensor is a high failure item but does not seem to be
related to your current problem.

> I'd like your idea of chasing down the grounds first.  Where does this
> system get its ground?  The one under the ISV on the valve cover?

yes, I believe so.

>  And what
> is the "frequency valve"?  Finally, the Bentley talks about an ISV
> controller.  What is that?

double wide relay, located in auxillary relay panel in the drivers knee panel
area.


I strongly suggest you look at SJM's documentation on this.
http://www.sjmautotechnik.com

HTH

-Marc-
87 4ktq
88 90q