Subject: Is it possible to repair the "Computer" (ICU)

[Huw Powell]

> The ICU controls the ISV, but I'd be willing to bet it is through a
> relay somewhere - an ISV likely takes more current than an ECU is
> comfortable with.

I don't think it uses a relay.  It most likely switches the ISV ground
on and off (fairly rapidly, the ISV is a "duty cycle" type device) since
a lot of Audi stuff works that way - constant power/switched ground.

> The temp sensor talks to the ICU also, and tells it to turn the ISV
> on and off - make sure the temp sensor and wiring are also good.

The temp sensor tells the ECU how much extra fuel to use to compensate
for being cold, and when to go into closed loop, and that's about it.

The idle switch is what tells the ECU to use the ISV to regulate the
idle speed.  I have not heard in this thread yet of that being tested.

I also can't remember the year or model, but I seem to recall this being
an NG or NF motor.