Bench testing Carrera Idle Control Valve

[scarceller]

Just sent you few docs that should help you figure out the ICV issue. If the ICV does not hum vibrate with key in RUN engine off you have an issue. Could be the valve, the wiring, the DME or a combo of either of these.

If possible test the valve in another 84-89 Car, very easy to do just plug it in and see if it hums in the other car. No need to install it in the test car, just wire it up.

NEVER use any other valve other than Bosch!

Originally Posted by Fangio246

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

[RobFrost]

Originally Posted by Fangio246

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

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=1142260&share_pid=12031768&share_fid=844&share_type=t&link_source=app


[quote name="wazzz" post=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.



I have a scope and an 88 Carrera. If I find time today I'll check it and report.

What's the frequency of the square signal?[/QUOTE]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.








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Sent from my SM-G988B using Tapatalk

[mysocal911]

Originally Posted by RobFrost

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=1142260&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.



I have a scope and an 88 Carrera. If I find time today I'll check it and report.

What's the frequency of the square signal?

Originally Posted by RobFrost

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.








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Sent from my SM-G988B using Tapatalk

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!

What's the idle valve signal look like?

[RobFrost]

Originally Posted by mysocal911

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!

What's the idle valve signal look like?

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.

Sent from my SM-G988B using Tapatalk

[mysocal911]

Originally Posted by RobFrost

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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Really, like where? You can also just add two 1K resistors to the valve connector, i.e. one from each center pin, to simulate the valve.
Then you can properly probe the two outputs without the connector on the valve.

[RobFrost]

Originally Posted by mysocal911

Really, like where?

This reply here:

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


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[mysocal911]

Originally Posted by RobFrost

This reply here:

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


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Nothing new here, i.e. no actual proper ECU testing, just more guessing! Time to send out for testing, e.g. Pelican Parts provides this service.
Good luck.