Sal, very good. Does the ICV have a spring force like center point or does it "float". Also.. I'm wondering if by slowly applying from 0-4vdc and 0 to -4vdc on the other pin and looking for non smooth movements is of any value.

Hi Loren,

I agree, the first test you should do is the one you mention or the one from the manual page I scanned above.

But if the in car testing fails it might not mean the valve is bad, it could be a wiring issue or bad DME (cold solder joints). This is why I came up with the simple bench test.

Now, what has happened on this thread is that folks wish to really fully understand how this ICV puppy works. I don't mind us doing some research if it helps better our understanding. I'm willing to entertain the idea of doing some research to learn more.

But I'm with you 100% that you should start with the in car testing first then
if you suspect a bad ICV bench test it. But if the in car fails and the bench passes you may need to know a bit more and this is where our research can pay off.

As always thanks for your input.

Henry,

The ICV just floats, meaning it sort of stays put where you leave it. If you bench test it and you can get a variable supply that is the best test. You just vary the voltage from 0-5v and the valve starts to move you can hear it plus you can blow into it while doing this. Drive it fully open then switch the leads and drive it fully closed. All the while listen and look for stick points. Remember this thread is about bench testing the valve. But you should have done in car testing as well.

So we have our answer! The ICV signal is a pulsed ground signal, someone has already done the work for us, see this thread:

http://forums.pelicanparts.com/porsche-911-technical-forum/346667-motronic-idle-surge-solution.html

Also, note that in John's post above his issue was a burned out transistor in the DME! He diagnosed the issue with a scope on the ICV control lines and found one of them completley dead while the other had signal. The signal to OPEN the valve was fine but the one to CLOSE it was dead, he replaced the transistor and fixed the issue.

It's issue like this that really do require us to understand these signals.

Many thanks to John.

I want to add this extra in car test data to this thread:

With engine at idle you can measure DC voltage between the center pin and the 2 outer pins and you should see 3.0 to 3.5vdc on each side. If both sides don't read in this range you could have a bad drive transistor in the DME or a wiring issue. Of course I assume the valve is good.

Note that the valve MUST be connected and functioning when you perform this voltage reading test. This means you MUST have a way to access the pins with the valve plugged into the harness. Easiest way to do that is pull back the rubber boot on the harness so you can expose the wires in the connector. Or use 3 test leads to connect the harness to the valve.

Great work!

As an aside, I believe there is another failure mode that wasn't mentioned: the ICV itself wears out. The ICV is a little motor and I think internal contacts fail or more accurately, the the part that they rub on (the commutator?) wears through. [1]
A mechanic friend told me they wear out, I've replaced them and had that "fix" the problem. I've also disassembled one and seen some wear but wouldn't swear that it was the problem. I might have a worn one kicking around that I disassembled.

[1] I Am Not Totally Sure On This. You won't hurt my feelings if you correct me!

Chris,

Yes, they do wear out from mechanical movement at the contacts. I have such a valve here on the shelf. You can easily spot this type of failure because once a contact no longer makes contact that winding goes dead. Depending on what winding it is it results in the valve going fully closed or fully open and you either get extremely low or high idle speeds.

In addition to this failure the valves sometimes just get dirty inside and they bind up mechanically but this can often be fixed with some carb cleaner and a few q-tips to help aid the cleaning.

I bench tested my ICV and it opens/closes fine. I can't see the test procedure noted above from SCARCELLER. Does anyone have it?

Hi Scarceller,

I just tested my ICV Voltage not at idle but with ignition on, not sure if engine must be running, but I got 5.3 and 5.8V between centre pin and the two outers. I check wiring continuity, and its fine. Does this point to possibly transistors on the board failing, and needing replacement?

EDIT: I started the car and tested voltage at idle. one sat at 3.5V the other at 9V. I also bridged the valve and got 4.0V and 9V. So looks like I need to open the DME and try pull transistors off...

Thanks

You need a scope for a proper test! Read post #20 in this thread. It's a simple test to check the valve drivers in the DME ECM.

First, basic simple test.
Remove the ICV from the car and hold it in your hand tight, snap your wrist in either direction and the valve should be able to be opened with snap of wrist. You should be able to influence the valve to close or open with simple hard snap of wrist. If that does not work the valve is mechanically binding. Also if it's dirty clean it with starter fluid and few q-tips.

Next, fully close the valve using wrist snap. You should not be able to blow air through it when closed. With it fully closed plug it into the harness in engine bay but do not install it. Now turn ignition key to RUN and the valve should be humming and vibrating. And the valve should now have opened a bit.
This first test proves the DME is controlling the valve and is capable of opening it.

Next, remove ignition key. Unplug the valve and now fully open the valve manually. With it fully open plug it back in and turn key to RUN. This will cause the valve to close some. This test proves DME can close the valve.

If those tests pass, the DME circuitry is likely fine and so is the valve.

Why do you suspect you have a ICV issue? Can you elaborate on why you suspect the valve may not be working?

Enjoy!

Great revival of an old thread. Very interesting to read and learn how to test the ICV (easy way, and proper way).

QUESTION: what is the purpose of the ICV? What does it do, or what is it really controlling?

Thanks!

Hi Scarceller,

Thanks for replying. I can confirm the ICV moves freely when flicking it, and tests correctly at 22ohm and 44ohm. Middle pin out puts 12V too. I have checked Pin 33 and 34 from ECU to plug in engine bay, and there is continuity. After completing your tests mentioned above, I can confirm valve moves to centre position in both situations. So this as you say, points to DME being capable of centering the ICV.

Why I think there is an issue is because the ICV doesnt seem to ever open fully or even pass mid way when engine is running.

After the first 45 second cold start sequence, the idle then sits at 600 rpm until car is fully warm, in which it then gets up to 800rpm.

When using the test port to centre the ICV (with engine running), it wont centre. The picture below illustrates this.

So I am just really confused as to why the DME is forcing a low idle at cold start. It could easily increase rpm, but forces the valve closed instead.

Thanks.


http://forums.pelicanparts.com/uploa...1677746892.jpg

Yes! Post #20 provided a simple test to eliminate both the valve & the ECM drivers. Did you do it?
The next test should have been to test for the idle switch on pin 2 of the ECM being closed.
I've seen idle problems the result of the A/D converter in the ECM having bad input resistors values, i.e. not sensing pin 2 properly, or a damaged A/D input.

It's NOT that difficult!

Tested all ECM pin outs, idle switch worked. Depressed the throttle by 1mm and continutity changed. When pulling the idle switch plug off when engine is running, idle speed shoots up.

How else should I be testing it?

Re-do the test in post #20. Again;

1. Remove the valve and fully close the valve & re-install and start engine without connecting valve;
a) idle is very low and almost dies
b) connect the valve - idle increases
c) idle opens properly, if not - bad valve or ECM

2. Remove the valve and fully open the valve & re-install and start engine without connecting valve;
a) idle is very high
b) connect the valve - idle decreases, if not - bad valve or ECM

Hopefully, the valve is not inserted the wrong way. The arrow on the valve indicates air flow.

It doesn't get any simpler that!

It doesn't need to be condescending.

Yes, would be nice to assume I am not a complete idiot haha

I also feel as if I am going in circles with this, not just you :)

All I can say is I have tested the icv valve and function as per post 20. It passes when engine is not running.

This is my predicament though,

When shorting the connector to centre the icv I get two different conditions depending if engine is running or not.

If I turn ignition to run, then disconnect the icv plug, then start the car, it idles at 800rpm.

If I start the car first, then bridge the connector, the engine runs at 600rpm.

I have visually inspected the icv in both situations, and when pulling the plug before starting the engine, it is centred. When checking the valve after starting the car and bridging, the icv is closed.

So I am very confused as to why, if the engine is running and icv bridged, it won't centre.

I am hoping I am an idiot and there is a simple reason for it. For now, I can't set base idle as the icv just closes when the port is bridged with engine running.

The test in post#20 requires the engine to run after manually re-positioning of the vane in the valve. Read the post again.
The idle when the vane is fully open before re-connecting should cause the idle to be close to 1500 RPM,
if the throttle bypass screw is adjusted properly. Once connected, the idle should be less than 1K, but not 600.
The other test requires the valve be fully closed manually and re-installed without the connector.
Once the engine is started, the idle should be very low, e.g. less than 400-500 RPM. When the connector
is then connected, the idle should be about 800-900 RPM.

If not, then the tests failed and there's a problem in the DME ECM or the valve.

Set the base idle to about 800 RPM with the jumper connected. Once the jumper is removed, then the valve can compensate for any engine load changes from the base setting,
e.g. the compressor or throttle undershoot. If this doesn't function, then there's a problem with valve driver circuitry or valve. Use an ohmmeter to check the collector (middle pin)
and to each of the other two pins on both darlington transistors. The meter polarity is key. You may have a shorted collector to its emitter or base.

Message for scarceller

I'm in the UK and have an 1988 3.2 Carrera Targa.

My idle was surging a few times and I naively thought it was the Idle Control Valve (ICV). I took mine apart and cleaned it and when I put it back on the car the engine continued to surge.
Whilst the engine was running I turned the body of the ICV and it stopped vibrating!
I assumed that I had broken the valve and so got a used replacement off ebay. On the car this replacement valve didn’t vibrate or work.
I then took the car to a specialist garage (shop) and they also couldn’t get the ICV working.
I purchased a new LOWE valve from Germany and that too isn’t working.

All three of the valves I have will click side to side with 3 volts applied across the centre and outer pins.

There is 12.2/3 volts across the ICV Connector centre pin and ground, plus around 10.5 to 10.7 volts across the centre and outer pins with the ignition on, car not running.
On a normal multimeter I have 12.6 to 13 volts across the centre to one outer pin with the engine running and 12.7 to just over 13 volts from the centre pin to the other outer pin.

My friend bought his scope over and it is showing a square duty signal sign wave at the connector (disconnected from the valve) with the ignition on.

We opened up the engine management box and non of the components appear blown and the transistors and diodes are not showing any open circuits.

How does the engine management reduce the 12 volt supply down to 3 to 3.5 volts to modulate the ICV as you state? If i’m getting more volts and the ICV isn’t working/vibrating what is the likely cause?

Appreciate your help
Thanks
Andrew
UK