Idle stabilizer electrical signal

[prebordao]

I would like to know what kind of electrical signal is used to drive the idle stabilizer, things like voltage, timing, etc.

I suppose it's some kind of pulsing, but that's all I know ...

Maybe this is a bit too technical, but can anyone give some pointers ?

[Porsche_monkey]

On the 74 listed in your signature?

[prebordao]

No, my 74 hasn't got one... But I thought of retrofitting one and would like to find the signals for a typical one as used in later versions (3.2 might be the earliest)...

[Raceboy]

It's not easy to retrofit because ISV's rely on PWM (pulsewidth modulation) signal which is basically switching +12v supply on and off very quickly. How quickly exactly is what determines ISV duty and thus idle speed (i.e. how much air it will bypass).

[ischmitz]

The ICV on a 3.2 is a three-terminal device. It has two coils with one common input and two individual inputs. One coil move the IVC the its open position and the other moves it to its closed position when energized.

The common input is connected to +12V. The signal to the other two inputs is a square wave signal 180 degrees out of phase. Essentially, one signal is the inverse of the other. It's a low-side driver with two outputs providing a path to GND. The frequency of the signal is fix at 80Hz. The duty cycle of the square wave determines the opening angle of the valve. At 50% it is in its centered position. The DME on the 3.2 uses a microswitch to sense when the throttle input is at idle. That is when the ICV actively regulates air. Once the throttle is depressed the ICV moves to its center position.

If you wanted to implement your own ICV driver you could use a NE555 in astable configuration with varying duty cycle driving two low-side drivers. You then have to decide what you want to use as input for the ICV. Somehow you need a feedback loop that processes the engine RPM signal and drives the duty cycle of your IVC while the throttle is at idle. You also need a sensor that tells your circuit when the throttle input is at idle. Fairly big project if you ask me. Hope that helps.

Ingo

[prebordao]

Thanks, I thought it would be something to do with PWM ...

I plan on using a PIC controller with inputs from the revcounter, oil temp sensor and an idle microswitch at the throttle.

It would act as an auxiliary air valve during cold starts and when warm would stabilize idle.

My car has already a microswitch in the throttle linkage, but I don't know what it's used for (idle, fully open throttle ?)

[ischmitz]

Cool. Sounds like a fun project.

Have you had a look at Megasquirt? They have tons of good information on various ICV configurations. There is actually a company that makes an aluminum block that can use a Jeep idle control valve and has ports so you can plumb it into your intake. I have used this setup on a Megasquirt controlled engine once.

Unfortunately, Megasqirt-II while using the ICV for cold start doesn't use it for idle stabilization. They felt it too much of a liability issue where the engine could rev uncontrolled if someone programmed Megasquirt wrong.

I believe the microswitch at the throttle body is for the cold-start injector. That injector squirts when the starter cranks and the throttle is closed. But it's been a while since my car had the 2.7.....

Ingo

[Porsche_monkey]

Originally Posted by prebordao

No, my 74 hasn't got one...

That was my point. Although apparently not well.