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Hi Folks,

I have been stuck on this high idle and finding information about the actual ICU and the ICV functionality in detail for a while.

I have tested the ICV by applying 12vdc directly and find that it drops my rpm to a stall. I am confident that the ICV is functioning. I have two ICU's, one is original from vehicle and the other is a used unit. Both have same part numbers - 002-545-33-32. I removed the back of the wire harness on the ICU to measure readings at the pins.

Current original ICU
PIN:
2 = 12v (battery voltage)
4 = GRD
6 = 12v (bv)
8 (not sure what to measure but there is no voltage)

pins 1 and 5 control ICV

1 = (no voltage to ground or to pin 5) but I get battery voltage to + terminal as if pin 1 were a ground
3 = 6.25~6.4 volts
5 = same as pin 1
7 = same as pin 8
9 = same as pin 8

The other used ICU that I tried had the same pin results except that across pins 1 and 5 there was .25~.30 volts.

Still have the high idle. I checked all the temperature sensors and grounded/jumpered them to be sure. Looking at other suggestions, I also replace the three transistors on the original ICU board and re-soldered what looked like a couple of cold joints, there was no change. It seems that the ICU is the problem, I want to verify and repair it somehow.

It would be great to have a detailed component schematic of the ICU so I can continue to test the parts on the board plus it would show me the functionality of the board. My scope is down right now but I can follow through with some other component testing. I have not found a reasonable price for a ICU yet, otherwise, I would just purchase another. I have two ICU's here and no reason why I can't get one to work, I hope. It would also be great to find or get an understanding of how the ICU and ICV work together and how the other surrounding controls are integrated in functioning all together.

Does anyone have any ideas, information or direction to share?

Much appreciated !!

'85 500 SEL 117.963
 

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did you check to see if you have voltage out of the female wire harness to the ICV?
 

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There is a threaded hole on the top of the ICV, which is covered by a plastic cap. I think it's actually an SAE 10-32 but I could be wrong.

Take a measurement of how much above the metal case the brass bushing is. Put a screw down the hole and GENTLY pull to add 1mm of height to the ICV and try again. That should fix it.
 

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That link has a great picture of the nut and bolt. This is a very easy way to fix a tired valve but be careful not to overdo it.
 

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I had 380sec in the shop with high idle like yours after eliminating the ICV and ICU and the wiring I found the problem to be a blown fuse in the OVP relay, replacedthe fuse and idle went to normal.
 

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I had 380sec in the shop with high idle like yours after eliminating the ICV and ICU and the wiring I found the problem to be a blown fuse in the OVP relay, replaced the fuse and idle went to normal.
That is a simpler check. OP does the idle go UP when you pull the IAC plug when the car is running?


Also, since you have two of these - when the car is running, unplug the IAC wiring and attach it to the spare IAC in your hand. It should start vibrating.

if it doesn't vibrate, you have a wiring or sensor problem.
 

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Discussion Starter #8
I had 380sec in the shop with high idle like yours after eliminating the ICV and ICU and the wiring I found the problem to be a blown fuse in the OVP relay, replacedthe fuse and idle went to normal.
I checked for power at the relay fuse and all is good. Also, there is battery voltage at pin 2 at the ICU.



That link has a great picture of the nut and bolt. This is a very easy way to fix a tired valve but be careful not to overdo it.
I suspect it is a metric bolt (M5 x .8), not a 10/32. I have a bunch of different sizes that I will check. My ICV has that brass cage inside another housing and looks as though there is a metal cap inside where the threads would be. I am taking the assembly apart so I'll have a better look at it.





This is one of the better links, thanks so much for it. I will run through some of the items that I have not thought of or wasn't sure that I could do, like remove harnesses while engine is running.




did you check to see if you have voltage out of the female wire harness to the ICV?
I did some further testing with this. At the "female wire harness", I tested the voltage across the ICV pins with harness connected and showed .30 volts. Disconnected the ICV harness and went across the harness pins that showed 0 vdc. It did not matter if the engine was cold or hot. I changed out the ICU with another I had, same readings except the only difference was that the disconnected ICV harness pins showed battery voltage when disconnected.


I also started the engine cold and hot with the ICV wire harness connected and disconnected, no change, still idles at 1500. I did a quick and sloppy smoke test to look for large leaks, no leaks.



Thanks for all the replies. I am not sure what voltages I should be seeing at the ICV and ICU with harnesses connected/disconnected. Though, I did see the voltage at the ICV should be about 5 volts which I am not getting. I have to find out if it is a malfunctioning ICU or if the ICV is dragging down the ICU. I have tested the ICV with 12 v and it seems fine but the resistance across the pins is out of range at 10~11 Ohms. With the voltage so low at the connected ICV harness, maybe the ICV is resisting too much making the ICU work too hard. I will try to check current.
 

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Typically normal at
Temp idle around 650, remove the electrical plug from the idle valve and the idle moves up to 1200-1600. You may want to open the plastic connector to be sure the solder of the wires are true. That harness cooks for 25 years and that wire typically breaks there, and the temp sensor up to where it joins up to the 4 pole temp plug, or almost
Even with the valve cover 6-8”
 

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I also started the engine cold and hot with the ICV wire harness connected and disconnected, no change, still idles at 1500. I did a quick and sloppy smoke test to look for large leaks, no leaks.
So this line makes me think the problem is not the ICV. Just to check - when the car is running, if you pull the connector at the ICV nothing happens? The idle does not go up? Do me a favor - take that connector and plug it into the extra ICV you have when the car is running (don't swap them, just plug it in in your hand). It should hum/buzz. Is it? If not, then for sure the problem is wiring.

Alos - is this a Gen2 car? There is a vacuum line going to the ignition module. Take that vacuum line off. IIRC there is a diaphragm in the ignition module that can sometimes go bad and affect the idle speed. I had this problem in my first Gen2 560SEC.
 

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A lesson in modesty. There I was driving down the road chuckling to myself for having avoided "high idle hell" when my rpm levels went from 750-900 to 1000-1500. Good thing I had just gone through this thread and the earlier one so as to have a beginner's understanding of what might be wrong.
1. First step was to see if the idle air control valve itself was stuck and I applied liberal amounts of "Gun Scrubber" to no avail.
2. Then I thought to move the internal valve using the screw and nut as shown in the photos earlier in this thread. But the 141-14-25 (also the 141-12-25 for US models) has the plastic cap and three spoked thingies (technical term) recessed about a 1/4 inch and there is no way to pull it out. Or am I missing something?
3. After that I followed the advice of those wiser than I, esp Corellian and Ian, and applied six volts to my recently acquired used IACV and it hummed. But when I pulled off the wire connector, it crumbled in my hand (33 years without change). (I also applied six volts to my spare IACV's (both bought used and they click).
4. At that point, it looked like the wires inside the connector had come loose also. So, that may be the source problem. I hooked them up to the prongs on the IACV with alligator clips and the engine running and nothing happens, except the motor continues at 1500 rpm. Or it may be that there is no electricity in those wires. Or it might be something else like the temp sensor and things that by now you will recognize are beyond me.
5. Meanwhile, returning from a day trip out of town and about 70 miles from home the alternator belt parted ways from the car. I knew this because all the warning lights came on, including battery (the one that glows red). I assumed I was going to run out of battery in the middle of Florida, but luckily we made it all the way.
Next step is to get the belts changed and see what happens. If the IACV continues on the fritz then leave it at the shop for a check of the electrics.
At least its not Lucas :). Any observations gratefully received.
 

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So the wires were thin and spindly and the plastic cap broke. get heavier gauge wire and solder them to the pins, splice them and solder up the harness and give yourself some slack. I submit that can be the problem to all 3 connections coming off that harness so consider replacing all of them. Your belts should all be replaced at the same time, and I am sure it will all fire up just fine.
 

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Also, you have to break that plastic cap off in order to adjust the nut. Just crack it open with a screwdriver. It won't come out and then go back in.

But get everything else sorted first.
 

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Well, the belts are all replaced, warning lights off, but still high idle. Since I think theIACV is good,next step is to check the sensors and the wires to see if there is not a short somewhere. Stay tuned.
 

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not even sure if we are talking about the same thing but my 85 sec idle was around 1000 and my mechanic mocked up this device to adjust idle manually
 

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not even sure if we are talking about the same thing but my 85 sec idle was around 1000 and my mechanic mocked up this device to adjust idle manually
I would love to see a write-up on that or instructions to explain what he's doing!! I suspect that's similar to pulling out the center pin as I posted earlier. But this seems like a REALLY good mod. Have him take some pics of what he does!
 

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Loosen the nut at base. And then the knob to adjust idle... I won't try to explain how he explained to me but something about some discs inside there that will move up down to adjust idle



Talking about idles....my 500sel which had top end rebuild. Chains. Camshaft etc last year which drives great and super responsive idles a touch low at 400-450... Since the rebuild. Don't know why... Second u touch the gas. It's golden.
 

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see post #14 below. It was not the ICV, nor was it electric connections, nor sensors nor vacuum. rather, the three years old ICU is the culprit. Replaced it today with a Euro friendly ICU (previous was US model) and RPMs have come down to normal range. Now just have to correct over rich fuel mix. Then replace coil, cap, rotor, wire and plugs; most of these are six years old. about time. Cheers.
 

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Well, my brush with "high idle hell" was not as difficult as I had expected. Issue was not bad sensors, electrical short, or stuck Idle Air Control Valve (IACV) as I had suspected. It turned out to be a bad Idle Control Unit which brought the rpms down and then a tune up (cap, rotor, coil, plugs, wires) and its starts much easier, is much smoother and idles at 650 in gear and 950 in park. I have my car back.

Now on to refreshing the EZL thermal paste.
 

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950 in park is a bit high, 650 in park is more like a target.
 
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