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Car Forum / BMW Cars / June 2005Anyone know how an Idle Control Valve is supposed to work?
When I warm up my 528e, turn it off, then just turn on the ignition, the ICV closes completely. Under these conditions, it's getting about 5VDC. When I turn off the ignition, it remains in the fully closed position. Is this operating as designed? > When I warm up my 528e, turn it off, then just turn on the ignition, the > ICV closes completely. Under these conditions, it's getting about 5VDC. > When I turn off the ignition, it remains in the fully closed position. > > Is this operating as designed? What does it do when the engine is running? That's more important don't you think? Do you suspect that it is malfunctioning or are you just tinkering? AFAIR, the voltage fed to the ICV is constant, but it is pulse width modulated to modify the ICV opening. But I also remember that ther eis more than one type of ICV and their functions may not be the same. A good test would be to run the engine at idle and then turn off the ignition. Now look at what position the ICV is left in. It should be somewhere between full open and closed. -Fred W [snip] > What does it do when the engine is running? That's more important don't you think? Do you suspect that it is malfunctioning or are you just tinkering? Something is wrong with the Fuel Injection or Fuel Delivery, as it's running rough at idle (cold/hot), hesitates when cold, and generally seems to have less verve than a year ago (when I bought it). I've been on this tack for months now, slowly eliminating one possible culprit after another. The problem has slowly been worsening over time. > AFAIR, the voltage fed to the ICV is constant, but it is pulse width modulated to modify the ICV opening. But I also remember that ther eis more than one type of ICV and their functions may not be the same. That may account for the low "battery voltage." > A good test would be to run the engine at idle and then turn off the ignition. Now look at what position the ICV is left in. It should be somewhere between full open and closed. I think this test would be difficult and maybe inconclusive because it's so easy to alter the position of the piston by jarring the unit (as in when I remove it to look at it). I could try it, though. Thanks, Adrian. > [snip] > [quoted text clipped - 25 lines] > so easy to alter the position of the piston by jarring the unit (as in > when I remove it to look at it). I could try it, though. What you describe sounds mostly like a lean condition caused by a leak somewhere in the intake. This is a very common problem with older bimmers as the rubber and plastic parts age and crack, lose their shape and seal. The ICV could cause irregular idle speed but would not have much effect once you touch the accelerator pedal. -Fred W > What you describe sounds mostly like a lean condition caused by a leak > somewhere in the intake. This is a very common problem with older > bimmers as the rubber and plastic parts age and crack, lose their shape > and seal. I have looked high and low for a leak. I've used WD-40, propane, and even a tube (as a listening device). The neighbors think I'm a lunatic, as they saw me with the tube to my ear listening to various parts of my car. The most hissing I heard was from the ICV. There is a small crack in the hose from the ICV to the manifold, but it's so small it can't be doing much - besides, I covered it with my finger and it made no difference. > The ICV could cause irregular idle speed but would not have much > effect once you touch the accelerator pedal. > > -Fred W If the valve is in the wrong position when not at idle, wouldn't that have adverse effects as well? Thanks, Adrian. >> What you describe sounds mostly like a lean condition caused by a leak >> somewhere in the intake. This is a very common problem with older [quoted text clipped - 16 lines] > If the valve is in the wrong position when not at idle, wouldn't that > have adverse effects as well? No it wouldn't, because the air that passes through the valve (even if incorrectly positioned) is *metered* air. This means the air also passes through the Air Flow Meter (AFM) and so the electronic fuel injection is aware it is there and sets the mixture correctly. You would have an incorrect idle, but an otherwise fine running car, if the only problem were the ICV. -Fred W I probably should mention that so far I've replaced the O2 sensor, distributer cap and rotor (another problem), spark plugs, fuel filter, and have tested the coolant temp sensor, etc. City mileage is down, but highway mileage is still in the 27-30 range - maybe off a bit since it used to be 30. Adrian. > I probably should mention that so far I've replaced the O2 sensor, > distributer cap and rotor (another problem), spark plugs, fuel filter, > and have tested the coolant temp sensor, etc. City mileage is down, but > highway mileage is still in the 27-30 range - maybe off a bit since it > used to be 30. > Adrian. Sorry if I missed the earlier part -- what are the symptoms, any besides mileage? A mulfunctioning ICV would cause running issues more than mileage issues I'd say. You've done most of the right stuff so far -- although I didn't see air filter mentioned. -Russ. > Sorry if I missed the earlier part -- what are the symptoms, any besides > mileage? -Rough idle (not very bad, just some missing. Hot or cold) -Check engine light - intermittent. Mostly comes on when idling, then stays on for a day or two. -Lack of verve -Hesitation - worse when cold, but it's there when warmed up too. > A mulfunctioning ICV would cause running issues more than mileage issues I'd > say. > > You've done most of the right stuff so far -- although I didn't see air > filter mentioned. Air filter _looks_ quite clean. I replaced it about a year ago. > -Russ. Adrian. See http://www.geocities.com/bmw535i86/text/idle_FAQ.html > See http://www.geocities.com/bmw535i86/text/idle_FAQ.html Wow. That should keep me busy for awhile. Thanks for the pointer. > See http://www.geocities.com/bmw535i86/text/idle_FAQ.html Great link. Bookmarked. Thanks, -Fred W |
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