Old Bosch mono ICV

[keith]

Hi All,

Please excuse any abuses of naming conventions....

Looking for some advice on elderly VW bits from early 1990s.

Hoping to use a Throttle Body from a Bosch SPI fitted to an AAU VW engine from a 1993 Polo.

This TB has two electronic units attached plus the injector/air temp (flow?) sensor.


IAC Question...

The Idle control valve pushes the throttle valve open by operating the pulley that the throttle cable fits around.
The idle control valve has 4 pins, two directly to a perm magnet DC motor and the other two are connected to contacts that seem to indicate when the plunger (that pushes the throttle valve open) is fully retracted.

Auto data shows the DC motor being fed with battery voltage and a 30% duty cycle. I'm worried that I may drive the motor too hard past its stops and damage the motor shaft helix or plunger gears. I could use the 'fully retracted' contacts to prevent over-closing the device but how would I prevent over-opening it?

I suspect I am missing something obvious here..... but if attempts by the MS to raise the idle speed fail, what stops the IAC motor (or gears) getting destroyed? Should the current be limited - but even then wont the motor overheat if always being driven against its stop (if it has one)?

TPS Question, I don't actually need to know this but am just interested if any one knows why they are configured as they are....

The TPS, (according to autodata) is operating correctly. As you would expect, there are two potentiometers connected opposite ways round. For the first quarter turn of one pot (and the last quarter turn for the other) the resistance value does not change. Any one know why is this configuration used? IE why not vary resistance for 100% of the travel?

Thanks in advance,

Keith

[Ollie8974]

Contact Mario Velotta Jr. He is a forum member.
Mario at the dubshop dot net

[mariob]

Although i am the wrong Mario, i have several cars around me with this idle setup. My approach to get it working was to use a separate microcontroller (simple 8-bit AVR in my case) to control the idle dc motor. The MS is configured to give me a simple pwm signal, which the new controller compares to the lower of the both tps pots. The second trick is to tell the MS when the idle-switch is closed. I realised this by simulating the tps for the ms and simply setting tps=zero if the switch closes, independent of the real tps position. This means you have to use speed-density as load algorithm and can't use tps for AE etc. All this sounds quite ugly but it worked quite useable on three cars so far.

I never saw problems of destroyed idle control motors as the motor is only allowed to move with more than 10% pwm if the idle-switch is closed. (the <10% opening is just used for rare cases where the idle motor drives out of the reasonable area while the throttle is fully closed) This protects the lower end as the switch will open before reaching it. The upper limit is not that necessary as you will never want to open the throttle that far and can use the tps to see where you are in this case. In general it is not necessary to drive the idle dc motor that fast as this will just cause oscillations and overshoot.

Best Regards, Mario

[keith]

Thanks Ollie, I'll contact the user you are recommending if things don't make sense.

Hi Mario,

Thanks for the advice.

Could you explain one more time for the hard of understanding;
Can the idle can be changed with just 10% PWM?
Do the contacts close when the IAC is open by 10%?

This car is LPG (LPG only - not petrol/LPG).

I'm hoping to manually adjust the IAC directly from a PWM driver via a DPCO relay (for reversing the motor).

I'm hoping I can fully close the IAC once the engine is running 'closed loop'.

Thanks again

Keith

[mariob]

Hi,

i can't give you exact numbers on how many % pwm you need to move the throttle but you will need a higher pwm-rate for opening than for closing. A warm engine may run on a fully closed throttle - at least this was always the case on my self-built throttle plates.

For better understanding you can do a simple test:
- wire up the "idle switch" to a lamp or LED
- drive the motor directly from the battery by short pulses generated "from hand"
- drive the throttle to a slightly opened position
- start the engine
- open/close the throttle by the idle control "valve" and see how the engine reacts
- play with the throttle and look at yout idle-led

Best Regards, Mario