Should the ICV leak a bit? (warning- bad language and a little bump...)

[genphreak]

Hi all,

Last night I handed my gf my (nicely cleaned) ICV. I asked her if she thought it was faulty, explaining that it should open and close to block airflow depending on what the ECU thinks at the time.

She took it with both hands and gave it a big blow. Pronounced that it was failing... no sucky though- she's a smart girl and it smells of petrol... (ok I lied about the 'both hands bit' :) )

However other people (thanks R) and my meagre findings on the web) are making me think a little leakage is OK. The reason I am still whinging about it is that the thing opens one gets a whack of alloy on alloy. When closing it it you get a nice soft thud (like there is rubber in there). As I cleaned it a year or two ago with carby cleaner I am worried a rubber might have perished and been eaten by the engine.

More on this issue in a previous post here... (http://www.bimmer.info/forum/showthread.php?t=22805) (BEWARE: Official boring post warning; absolutely no porn!)
:) Nick

[Javier]

Can the ECU set the idle low enough or it stays up or waving?

I do not believe that the unaccounted air will be a problem, as ECU should learn from feedback signals and adjust itself.

Javier

[31Hertz]

Even if you are flowing a bit of air through the ICV; it is after the AFM so the air is metered (ie not unaccounted for). I just removed my ICV to clean it, and its natural (no voltage) position was neither open nor closed but in the middle. I rotated it gently to check for free movement, and at its extremes it sounded like metal stops not rubber... But the test you describe is semi-exciting... I did not perform this test myself, as my wife was unavailable at the time.:p

[pingu]

According to this link:
http://www.geocities.com/bmw535i86/text/idle_FAQ.html
on:
http://www.e38.org/e32/

"The solenoid valve in the ICV does not entirely control the air flow though it; an adjustable bypass system within the ICV allows air to flow through it even when the solenoid valve is completely closed (hmm...a bypass system within a bypass system!). "

OK, so that explanation is from a 7 series site (and may not be applicable to the E34) but I'd be surprised if all the idle control systems didn't work in much the same way.

[rob101]

But the test you describe is semi-exciting...
Now i am worried:p i think the throttle is slightly open anyway and at least on the old school L-jetronic there is an adjustable screw for idle (which runs parallel with the icv (if you follow my electrical analogy)) presumeably to compensate for wear.
I'd assume that the ECU probably compensates for extra wear on the newer systems anyway. since the screw is usually out on the L-jet i'd assume there is a little bit air flow through.

[Blitzkrieg Bob]

the ICV for leaks, but first maybe she should practice on me.

[t_marat]

According to this link:
http://www.geocities.com/bmw535i86/text/idle_FAQ.html
on:
http://www.e38.org/e32/

"The solenoid valve in the ICV does not entirely control the air flow though it; an adjustable bypass system within the ICV allows air to flow through it even when the solenoid valve is completely closed (hmm...a bypass system within a bypass system!). "

OK, so that explanation is from a 7 series site (and may not be applicable to the E34) but I'd be surprised if all the idle control systems didn't work in much the same way.
I guess the recommendation there not to clean the ICV is no longer valid?

[genphreak]

Now i am worried:p i think the throttle is slightly open anyway and at least on the old school L-jetronic there is an adjustable screw for idle (which runs parallel with the icv (if you follow my electrical analogy)) presumeably to compensate for wear.
I'd assume that the ECU probably compensates for extra wear on the newer systems anyway. since the screw is usually out on the L-jet i'd assume there is a little bit air flow through. Yes that's right Rob. The problem comes down to dirt and data sensing, or plain malfunction. On Motronic all the adjustment is via the ICV (automatic) and the AFM flap (set at the factory for CO levels and flap (airflow) calibration). All the mechanic can do is check the throttlebody butterfly closes cleanly with the right gap as the ECU looks after idle speed from there.

Thanks for the replies guys. All right of course. The thing taht is weird is my ECU is deliberately reving the engine at 750rpm when stationary in 'D' (albeit from the dash tachometer- I really need a diagnostics engine tacho to check it accurately) which I think should be more like 650. However as we know, the ECU decides all such things. I am worried that somehting is affecting it. If I reduce air through the AFM flap at idle it will might make up for it, but maybe I need to do the whole AFM calibration prcedure. It's either the AFM or a leak.

The fact remains though, if there was anything slightly wrong with the ICV this could easily be it... :) Nick

[genphreak]

Yes its a good writeup that.

Its a pretty old write up, from years ago describing mainly the older ICV systems- a lot is similar though, but nothing to do with the PCB controller is the same.

I will leave assume the ICV is perfect and recalibrate the AFM- It must be the culprit. A MegaSquirt was gonna fix all this, but as of yet there has not been the time to do it... bah, and here I go again- fixing what is going to be replaced... :) Nick

[genphreak]

the ICV for leaks, but first maybe she should practice on me.Would she do a better job than my girlfriend though... :) I think she might...

[rob101]

check your current to the ICV, i think that is the way it is meant to be. rather than checking the idle speed.
very involved ended up disconnecting the bastard on the e28 too much BS
now she runs like a charm
idles a bit high though (1200 rpm) lol
i would expect that the idle speed in D would be a bit higher if the idle is correct in Neutral and Park then you should be right?

[genphreak]

check your current to the ICV, i think that is the way it is meant to be. rather than checking the idle speed.
very involved ended up disconnecting the bastard on the e28 too much BS
now she runs like a charm
idles a bit high though (1200 rpm) lol
i would expect that the idle speed in D would be a bit higher if the idle is correct in Neutral and Park then you should be right?Actually it looks like 750rpm is what the ECU aims for in gear or out. It will adjust the revs when load is put against the engine at idle. And I found out the TPS also tells the ECU when the throttle is wide open. Weird, why then have a kick-down switch under the accelerator pedal? Looks like my ICV is fine. I'm back to blaming my charcoal cannister after doing a full check of everything, and tuning the AFM. Whata job. PITA stuff. Still, there has to be a reason for this... :) Nick

btw; Your e28 is not motronic i think- no? L-Jetronic isn't it? Earlier Motronic have a idle control system controller in the glove box, this was a poorly made circuit that needed careful attention in many cases I believe