Yet another high idle question

[rsmartin]

more progress. found another vacuum leak. a plastic line that runs underneath the ICV and connects to one of the thermal? switches was disconnected. so now it's idling about 900 RPM in Park. getting there!!

[Harro10]

Where was it disconnected? That bank of vacuum lines under the ICV?

[rsmartin]

circled the connection where it was disconnected on the attached diagram

[ctaylor738]

And as a bonus, you may now have proper venting/burning of vapors from the gas tank.

I believe that vacuum connection opens the valve that allows vapors to be drawn into the intake manifold. It is controlled by a temperature switch because it doesn't operate until the engine is warmed up.

[rsmartin]

yeah, it's an interesting circuit. i'm gonna do some testing to make sure it's working OK.

is it normal to have pressure built up in the gas tank? often when opening the tank for a fillup, a whoosh eminates from the filler neck.

[Harro10]

That line and the ones in that area all look good on my car. The ICV seems to check out ok. I get 4 volts across the pins and it opens smartly when I apply 12 volts to it. I will keep looking for a vacuum leak. There is a white vacuum line that disappears out of sight toward the firewall about a couple of feet below the linkage center passenger side of the car. I wish I could check that one but aside from taking apart the linkage I do not see how a human being could get to it. I can not even see where it connects to the firewall and am worried that it my not be connected to anything.

I have a used ICV and a used ICU coming (ordered before the tests - there was a delay getting the meter) and I will try swapping them out but after following Chuck's advise I believe my car's problem is probably vacuum related.

RS- I also get that pressure relief when I open the gas tank. I believe it is normal.

Thanks RS and Chuck


P.S. Thanks for that vacuum diagram. I am going to print and save it.

[TAP]

I recently had a high idle issue that turned out to be stiff linkage. It was an easy fix. Most likely not your issue but you may want to clean and lube the linkage while you're in there. Hope you find your problem. I will probably need the info myself someday. Also, please explain how you get your son to return your tools. I have yet to find a solution to that one.

[Harro10]

It turns out that the meter I lent my son is somehow MIA. But he has since bought his own so I borrowed his. Let's see if he gets it back.

[rgp717]

Hi, I hope to revive a portion of this thread. I too am in high idle hell (that was an excellent article and got me started).

I think my problem is in the minority, I believe my ICV is bad and not the Idle Control Unit, and here's why: (1) I measure 3.7V across the pins of the ICV, (2) I removed the ICV and put 12VDC to it, and nothing (no clunk or noise whatsoever), and (3) moreover, I put my toy train power controller on the ICV, and adjusted the V from 0-12 DC, and no change whatsoever in the high idle (I read this trick somewhere ... it's a good one).

OK, so I got another ICV off of eBay (it's used). It seems to be good but I think it's bad too. The good: If I put 12 V to its pins, I hear/feel a clank. If I install it and put variable voltage to it via train power controller, I can make it work; that is, I can apply more and more voltage and bring my idle down to 900 (or less). BUT, when I put the connector on, and check the voltage across the pins, with the connector slid back ever so slightly, I read only 1.2V (and the idle is 1500).

Now on my original ICV, I measured 3.7V, so I think the connector is good. On the eBay ICV, I measure only 1.2V (and I cleaned the pins too).

So, my question is: Do I have another bad ICV, or should I look elsewhere?

[ctaylor738]

The valve is a frequency valve which means it is either open or closed. You can measure its operation by taking voltage readings, but you can't make it work like it is supposed to by varying the voltage.

I would say that the eBay valve has some resistance in it, which is dropping the voltage reading. Or that your control unit went suddenly TU. If you can get back to 3.7 with your old valve, the control unit is probably OK. So if you can't find any vacuum leaks or air leaks, you need to bite the bullet on a new valve, or at least test with a known good one.

[Harro10]

I received the used Idle Control Valve and Idle Control Unit. I installed and checked the valve and there is basically no change in the high idle situation. I am reluctant to install the newly arrived unit. The part# called for in my 1989 560SL is#0045451132. The part that arrived is #0045451032 which seems to be for a 420SL or 500SL. I question how much I might learn about my high idle problem by knowingly installing an incorrect part. I am also worried about causing further problems to my car. Does anyone here have any opinions about whether or not these parts are interchangeable?
Thanks

[Harro10]

A very big thanks to the board.
I tried dpetryk's magic trick of adjusting the brass threaded insert inside the Idle Control Valve. He posted the technique in this thread:
Idle Speed Air/Control/Slide Valve Confidence Check
in post#s 12,13,18 and 35.
I adjusted the insert about a 16th of an inch outward and reinstalled the valve. The idle on my 560SL is now about 600 RPM in gear and about 650 RMP in park. This is a big improvement over the 750 and 1200 RPM it was previously. It is even up and down shifting much smoother.
We will see if this is a long term fix but for now I am one happy camper.
Thanks all

[rgp717]

Chuck, thanks for the tips. It was definitely the Idle Control Valve. I got yet another replacement ICV, and the idle is nice, low and even (500-ish in gear, 650-ish in Park/Neutral).

Just a note to others in high idle hell: I never gave up on my old ICV; when I first pulled it, I sprayed it over and over with carb cleaner, until it no longer ran dirty. Then for 5days, I would spray a little WD40 in there, and shake it for 5 minutes or so. On the 3rd day, I heard a rattle for the first time. Immediately I put it back on the car, and no more high idle hell. It just so happens that the 2nd replacement unit arrived (literally) at the same time by postman. So, now I have a spare.

Chuck, I'm not sure what the toy train controller is doing exactly (it may not be varying voltage, but rather varying AMP). However, if I connect the first eBay ICV to the toy train controller, and turn the train power nob, I could make the ICV work. The ICV would not work normally on the car (only 1.2V across pins), but the toy train power unit could make it work (3.7V across pins).

I still think the first eBay ICV is bad, as it won't work when placed on the car ... but at this point, I'm good. So, now I'll add the following to my routine car care; clean and oil up the ICV every so often (I'm thinking annually).