Mrmerlin

Here are some pictures of an ICV that looked new on the outside and the inside was filled with corrosion,
NOTE this was after an intake refresh had been performed.

Best to test the ICV to see if the shaft will turn freely,
this one was frozen, if it has stiction then replace it.

I got a new ICV , Bosch part from Auto zone 138.00 including shipping,
it didn't come in a Bosch box.
Now the engine idles as it should.

NOTE the S4 ICV is a non friction type unit,(so it could last forever if it doesnt get corroded)
so, it has no brushes that will wear out like the 85/86 engines have,
they are not interchangeable

dr bob

When the LH sees the closed throttle switch .and. engine speed is above ~~1200 RPM (indicated on my car anyway), the LH stops fuel flow to the engine. Thus the 90 MPG display on '89+ cars. The action of the ISV is related, but as an effect rather than a cause. The ISV is only active when the throttle switch is closed.

dr bob

Stan, That looks like water puddled in the ISV. I guess we need to drive the car hard enough each time to get the oil up to temp, and boil all those combustion byproducts out. Including the water.

Cheburator

I still think that you won't see 90mpg if you have a correctly working throttle switch AND a faulty ICV...

Alan

That is completely wrong. As others have said the ISV has no part in this. The 90MPG readout is a default value substituted for infinity. The only way you get there is for there to be no fuel flowing - this happens only in the over-run fuel cut-off mode. This requires the TPS to be telling the ECU that you are completely off the throttle and for the engine rpms to be up (not at idle).

In this mode adding a little air (or not) makes no real difference to the engine - there is no combustion happening. Issues with the ISV really only show up at idle, if you aren't getting to 90MPG during @ speed overrun then the TPS is most suspect.

Alan

FredR

Alex

If the shuttle is gunked up idle is at best erratic. When I had this problem the engine kept dying on me at the pilot air was cut off- as in the shuttle was not opening. On the other hand if it is stuck in a fixed position somewhat opened it may well cause the tickover to race a bit.

Once the brain is told the engine is now in the idle regimen by the idle switch closed position, the brain then looks at the rpm's and send a signal to the stepper motor to respond. Stuck solid it cannot go anywhere but it may be possible that a small degree of stiction may create a situation where the shuttle will not move until more signal is generated by the revs moving further away from the control point. Thus may explain why some folks report experience a surging in the revs at idle.

When this happened on my S4 I was told I needed a new ISV. I removed mine, cleaned the shuttle with a clean white cotton rag until I could see no more carbon on it, gave it a squirt of WD40 and it still works to this day. Now, over the last fews days, I noted a minor surge- maybe time to clean again. A bit of a bugger as I had the thing out only a few months ago.

Unless I am wrong, the 90 mpg should show up if the idle switch is working as that is the trigger to shut off fuel on the overrun until the revs have dropped to near idle if my memory serves me correctly..

Regards

Fred