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Discussion Starter · #1 · (Edited)
Been enjoying really great improvement in the idling behaviour on the C20XE, but any engine using this type of ICV should benefit from this readjustment.

With the stock adjustment it starts with a small opening, then closes first, then opens up again, and in this area it can fully open. The small opening is said to provide air in case of a wiring/ICV fault, so it still runs.

The change is to readjust it so this emergency opening remains at the other end of the valve, so in case of a fault in the wiring/ICV it still runs, but the trick is in the valve never fully closing at all, which is, according to a few (including a Vauxhall technician involved in the discussion here) totally unnecessary, even unwanted.

Most these engines now and then have the tendency, when the throttle is released fully (when shifting, when stopping, manouvring etc.) to go too low in revs, sometimes almost stalling, then the ECU detects and corrects, revs first go up in a burst and then stabilise.

With this mod this effect is completely gone. The revs may go down a tiny bit slower, but very acceptable, and once down they tend to be more stable too. Plus the whole transistion towards idling goes very very smooth.

Mind you, the grub screw in the side of the ICV is very well bonded with epoxy, and needs to be very well heated with a good gas flame. Also beware not to heat up the whole ICV, as there are plastic parts inside too. Apply the gas flame directly to the centre of the grub screw, and every now and then scrape excess epoxy away with a watchmakers screwdriver. Use a nicely small one that can also empty the allen key hole, right up until the allen key fits in nicely. Then adjust with the engine running with the ICV unplugged, until the revs are about 900, to keep a little adjustment range for the ECU. Then apply some nailpolish to lock it again and plug it on.

While you are at it you might want to relocate the ICV as well. I've drilled and tapped a hole in the back of the throttle body, under the butterfly, at the back. Then bolted in a 90 degree knee with some thread bond. And off course I put a plug in to the hole where it used to be, and ordered a custom hose from Roose to plumb it back on the SFI box. Obviously the TB work needs to be done off the engine, so remove it first!

Enjoy a smooooooth idle for once!:thumb:
 

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Discussion Starter · #2 ·
There's an interesting pic I found with Google that shows how it is NOT working properly IMO.



So the idea is to adjust it beyond the fully closed point, so it still runs when it goes dead, but never completely chokes on itself.
 

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Discussion Starter · #4 · (Edited)
Good stuff, someone make this thread a sticky!
May be a good idea, although I would first like to invite any who try it out to report if the improvements are also experienced. I would say this is likely, regarding the pile of similar idle issues reported in numerous threads on numerous fora. Where cleaning is always said to be the solution (and yes, it can help if it is smudgy, hence the advise to relocate it) but most just went on to live with it, or sold their cars and went on bad rapping Vauxhalls...This valve isn't just used on Vauxhalls, but also Mercs, Lambos, Ferraris, Porches, Saabs, Lotuses, Opels and many many more, so spread the news!

I've just had a nice early morning drive, with everything stiff frozen, doors barely opened, glad I covered the windshield and side windows, but the engine? Fired up instantly, idled smooth as butter, and went like that all the way from the first seconds on. I'm convinced!
 

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Discussion Starter · #5 · (Edited)
Fun detail to mention was the surprisement of the technician at the Opel garage, he knows his stuff, knows how to use a Tech box too, which is becoming rarer by the day. He knew about the idle problems and I discussed it with him a dozen times, drove with it and agreed it was not great. Then we concluded I should bite the bitter pill first and replace everything that was old, which was literally everything off course. So I bought many new original Bosch, many through the Bosch exchange program, spent more than a thou to have all the electrics renewed top to bottom. And? Yes it ran better, but didn't solve the idle issues completely.

Last week he had another drive, told him what I had done afterwards and we both discussed it some more and could only conclude it had to be a misjudgement of some kind from Bosch. The valve should not need to fully close.

We also went through the whole vacume system some years back, and already found out the sump ventilation mod, by drilling the small tube to 2 mill helped, but apart from that everything is original and functions as it should. All the hoses are brand new made by Roose, I tested the vacume system and there are no leaks whatsoever, which would also only worsen the ICV issues, since leaks make the "fully closed" position "less closed" obviously. Only when you would introduce more air through the sump ventilation (at least metered air) it would quickly bring the idle speed out of range for the ECU to correct it.
 

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Discussion Starter · #7 ·
While we're at it, here are some pics of the relocation of the ICV as I did it. It's not the nicest location when it is in a Corsa, but there are definitely more options where holes can be drilled and tapped, as long as it is under the butterfly it is fine...







It's not sticking out internally, to minimise airflow issues, and it is threaded in, then bonded to sit firmly with green loctite.

These are fairly old pics too, still using a botched hose, and I eventually pointed the knee upwards for even more convenient access. This was already with the brand new ICV though...
 

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Discussion Starter · #8 · (Edited)
Also need to mention, that due to the original location if there is oil in the intake it will reach the ICV quite easily, and any other dirt or debris will also, so the sticking valve troubles are very real! Cleaning and lubing with a good dry lube, at best teflon based, like finlube from interflon resolves any issues effectively, but when the ICV is not relocated, and crank ventilation is not breathing well, only shortly.

Part of this issue is due to only one way active travel, and spring loaded return. An answer of Bosch to this is the three wire model, that doesn't use a spring, and has two way active control. Unfortunately this won't be a straight swap on our ECU as it doesn't support it. Then again, if the three wire model gets gunked up you might only notice it when it's really bad. On ours you will be alarmed a lot sooner. With healthy crank ventilation you won't see any problems any time shortly as there will be NO OIL in the intake whatsoever! That'll be a next post... and I've posted this before, also on other boards...

 

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Discussion Starter · #11 · (Edited)
Amazingly detailed write-up, thankyou :)
Thanks! And I'm not even done yet, just gathering some more info and pics.

Why did you move it?
Two reasons, function and convenience.

Function: Oil drips down, and dirt drops down, so the higher you can place it the less trouble you can expect.

Convenience: This valve is used on many engines, but the C20XE must be the one where it is placed at the worst spot you could possibly think of. Why? Don't know. I know I've got no regrets placing it where it is now, and I know I've had many troublesome hours spent removing and placing it where it used to be. Including one time I dropped it and forgot to remove the battery earth strap, and had just cleaned the manifold with carb cleaner. It fell on the starter + and that created a big spark, then the cleaner ignited in my face scorching all my facial hair. Looking back I can laugh about it, but it was very stupid LMFAO.
 

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Discussion Starter · #12 ·
Here's roughly the position mine has now:

 

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Discussion Starter · #14 ·
How do you save a post if you can? As this could possible help me out
You can save the link, by copying the link towards the post number (top right in the dark grey area) you can also make a screenshot, or email the link to yourself, or copy the texts and paste it in a Word document, then save the pictures and add them in between.

There are many options.
 

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Discussion Starter · #16 ·
Your back, how you been?
Yes, some permanent hardware installed that will need some explaining done every time I pass the scanner at the airport, but yeah, I'm as back as I'll ever be I guess...:lmao:
 

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Discussion Starter · #18 ·
Doesn't really matter, the final adjustment depends on your engines leak on crank ventilation and through the small nooks and crannies of the throttle body. The adjustment is as I described done unplugged, basically this enables you to adjust the idle by hand. Obviously the eml light will be on, and the ecu will raise the voltage on the connector to max so beware of huge revs if you plug it back on. Best not do that with the engine running. So therefore you adjust to around 900 revs, so your ecu can still tune the revs lower if it should want to.
 

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Discussion Starter · #20 ·
After many miles I still stand by this adjustment method by the way, I can not fault anything about how the engine responds. If I must describe the way it runs, I would say just buttery smooth. Idle revs are 100% stable and incredibly consistent. Off course the engine itself is very healthy and all functioning and original (crank ventilation works as it should, so no oil in the intake AT ALL!!)
 
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