Originally Posted by Fangio246 (Post 11972836)

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

Originally Posted by Fangio246 (Post 11972836)

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

Originally Posted by RobFrost (Post 12032301)

Andrew, did you get the square signal on both end pins? I'm only seeing it on one, and am trying to determine if this suggests it's the DME. See the trace here:

https://r.tapatalk.com/shareLink/topic?url=https%3A%2F%2Fforums%2Epelicanparts%2Eco m%2Fshowthread%2Ephp%3Fp%3D12031768&share_tid=1142 260&share_pid=12031768&share_fid=844&share_type=t& link_source=app

Originally Posted by wazzz;=12031459

Others will probably shime in and confirm or not, but I think you should indeed see pulses on both sides. So if one side is dead, this might be the sign of a dead transistor inside Motronic. One of the ON588 Darlingtons referred as T560 or T561 on the schematic. <br />
<br />
I have a scope and an 88 Carrera. If I find time today I'll check it and report. <br />
What's the frequency of the square signal?

Originally Posted by RobFrost (Post 12032301)

Hi, I scoped both together versus the engine as ground, it shows 0.5V pulses on one and not on the other. I was hoping to check it at over- and under- revs, to see if the other started showing a signal but before I could the engine speed started fluctuating wildly. I suspect the ICV piston was oscillating within the valve.<br />
<br />
https://uploads.tapatalk-cdn.com/202...687bff1eeb.jpg<br />
<br />

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Originally Posted by mysocal911 (Post 12032618)

As mentioned in the following link (post #6), you can't use a scope to properly fully check the air valve signals without the valve plugged-in!

http://forums.pelicanparts.com/porsche-911-technical-forum/1142260-whats-idle-valve-signal-look-like.html

Originally Posted by RobFrost (Post 12035366)

I don't know if you noticed but there's a contradictory claim in that thread suggesting you can, by putting it on bypass. Not categorical, though. If I can validate that claim it'll be useful to me and to others.

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Originally Posted by mysocal911 (Post 12035515)

Really, like where?

Originally Posted by RobFrost (Post 12035590)

This reply here:

https://forums.pelicanparts.com/showthread.php?p=12031881


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