BC

The S4 has one, - is it three wire or two wire? I can't seem to get it back (including the TB and wire harness) from a contractor - and I need to buy one for the megasquirt project on the 78.

The arly cars had a temp controlled one. No powered motor, but a plug to reference the WUR or cold start valve I believe.

With the three or two wire ones on the S4 - are there differences as to how they are triggered? Can t hey move back and forth with different voltages?

I'm using the Megasquirt Fast Idle control output for the Ford EDIS distributorless ignition, so I have to figure out the idle air myself until MS II comes out.

I was thinking of doing a cockpit switch or **** that I could set the idle at when I needed to up it a bit or reduce it. Essentially I guess the two wire is an on/off, but the three wire has to be a stepper motor where it is controlled finitly by voltage?

Thanks

John Speake

Hi Brendan
The ISV in the 87 onwards engines is a two wire. It has a default spring biased position. It is moved from that position by a 100Hz 12v amplitude square wave. The mark space ratio is varied to move the valve to the required position.

Regards

BC

WOW! Thanks John.

So what do you think a 3 wire would do?

Can I go to digikey or Radio Shack (uh, think English - Like electrical stuff, wires, relays - all in a walk in store. My wife said Comet, but thats not right I think) and get these 100mzh relays and a **** to vary that?

BC

John Did you see my reply?

Tony

If it helps brendan, my S4 idles and starts fine with out the Idle valve plugged in! Has done so since i put the SC on it! Just one cold day here in vegas it stumbled a bit, but the next attempt it caught and began to idle fine.


I used Johns tester to run the idle adaptation sequence on it yesterday. Pretty slick! But i think the factory program doesnt have enough "calibration" in it to adjust for the SC sitting on the top. It did the adaptation cycle then it settled at a nice rock steady 1300 rpm! I unplugged the Idle valve conector and it dropped and settled rock steady at 7-800rpm. Im going to unplug the brains agaon today and let the LH unit adapt itself rather than using the factory settings that the diagnostic unit provides. Im sure it works slick on a NA S4!

.

Rich9928p

Brendan, the 100 Hz signal would be produced by a wave generator. I'm not aware of any part like a relay that outputs a square wave. The LH injection controller outputs the signal to the idle speed regulator. It isn't always 100 Hz, if it was, there would be no idle speed regulation, the regulator would be held in only one position. The frequency is varied (lower or higher) to increase and decrease the amount of bypass air into the intake manifold, which is how idle speed is regualted.

So what you would need is to design and fabricate a control system that looks at the idle RPM and varies the frequency output to the idle speed regulator "in real time" to keep the RPM within the specified range.

John Speake

Hi Brendan,
Sorry, was off line...I have no detailed knowledge of the Megasquirt system.

I have to disagree with Rich. It is the mark space ratio that varies, not the frequency.

BC

Hmmm. Well, the megasquirt probably does not have this adaptation. The AEM for my S4 will not need one probably though - as that computer is supposed to be able to catch the idle without air control. We'll see.

I guess I may have to use the passive iac from the early cars.

BC

After all the other changes that I have made to this motor in vacuum control, spark, fuel, intake, I hesistate to go past a KISS ideal on the IAC. If it was a "**** with power switch" idea, then I would have done it, but what you and John have described seems way more complex then it needs to be to control idle in Southern CA. I may as well bolt on that ugly passive IAC that is controlled by head/coolant bridge temp.

BC

Thanks for your help guys.

John Speake

Yes, KISS is good :-)

928mac

Dug this old post up as I don't think my Idle control valve is working.

Can it be tested off the car and how is that done to verify that it works correctly.

Rich9928p

The idle control valve/idle speed valve provides the much higher RPM for cold operation as well as managing warm idle speed. If the engine RPM is higher for cold start, that is pretty good evidence that it is working. If your problem is warm idle regulation, but not cold start idle that could indicate a different problem. A failed temp II sensor or bad connection can provide problems as the engine temperature is a major input for the idle speed valve operation.

A good shot of carb cleaner into the intake line may help free it if sludge build-up is the problem.

The idle speed valve is located underneath the intake manifold and isn't accessible for observation. As far as I know, the intake manifold must be removed to gain access. After all that work, you may as well replace it.

If you have an oscilloscope, you can monitor the control signals, the LH module provides the ground for the ISV at connector pin 33, it is a 100 Hz variable duty cycle signal. But if the idle speed valve is stuck that won't tell you if it is working.

Rich
'93 GTS Cover Girl
'87 S4
'79 5-speed rescue
'79 Euro 5-liter track beast

SeanR

Best test for it is to have a Bosch Hammer available to plug in.

If you shoot a burst of carb/brake/maf cleaner in the intake you risk the chance of a fire, it's not a smart thing to do due to intake back fire and MAF hot wire igniting it.

There's been a bit of talk about shooting WD-40 in the vacuum hose in to the MAF boot to loosen up an ISV, I've seen this only gum stuff up and the WD-40 pools at the elbow going to the MAF boot. Anyone who's had the intake off will see how futile this is.

Mrmerlin

Here is how they work and what can go wrong, pictures included

https://rennlist.com/forums/928-foru...?highlight=ICV