Low voltage at Idle Control Valve - Mercedes-Benz Forum
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#1 (permalink) Old 10-26-2008, 10:28 PM
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Unhappy Low voltage at Idle Control Valve

Ok I have been working on my cars cold start and sporatic idle problem and tonight here are some of findings.

The problem. When I start my car it jumps to 1300rpm, and dies or idles at 1000 rpm. But it does not go down to 750 rpm after 28 secs, like mentioned earlier. It just idles there and then I shift it drops to 600 rpm and then the car shakes. Once shifted back to park or nuetral it goes to 700 rpm. It is like it tries to make up for the load, but it just can't.


When the car is cold I am only getting 2.15V from pin 2 on the connector at the ICV while using a hard ground. This is the same it I test from pin 1 to pin 2 on the connector.


I did the bench test (mentioned in stalling again thread) on the OVP and it all checked out good. 12 Volts at each pin. The fuse on top is also good. Also the OVP is seated all of the way in the connector.


I started the car and checked and there was 14V going into the OVP, but I don't know if that is relavant to anything.

When the key is turned on I can feel both the OVP and the ICV click.


Any idea whats going on here?
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#2 (permalink) Old 10-26-2008, 11:06 PM
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mmm Go back to to the ICV pin out test. Look up what pin is going to the ICV. Pull the OPV and on oHms check the from the pin hole in the base of the OPV and the other probe at one or the other Connector right at the ICV. You're looking for a bad wire or maybe the connector itself.

In my mind, IF you have 12v's at the OPV, you just have to have 12v's at the ICV , right? If a good circuit I would think it would be impossible to be different. Normally a problem is anything up around a 1 volt drop. Acceptable is zero to 0.1 v or up to 0.3 across a switched circuit like a relay. This from my manual.

Also test the other wire for a good ground. Infinity on the meter to any good ground.

Another idea... I read somewhere not too long ago of someone who had a crack in the OVP base plug. Sometimes it worked and others times,,,,

Also check the ohms of the Heater section on the ICV. Unplugged Ohm meter across the terminals on the ICV.. sorry, you need to look this up in the manual as I don't recall. I was thinking it should be 12 ohms +- 3 but I think it might be 40 ohms, so look it up. If you can't find it, I will look it up. This tells you if the Heat coil is good or not.

OH, I don't think this is your issue but you want to make sure you have a good battery in the meter, if very low you get false reading at times, usually on Ohms though. You seem to be getting a good reading of 14 running, so not likely.

The only other thing I can think of and I really don't have clue how it works exactly. Is how the idle is controlled when a new load is added like the A/c. On mine I know the idle drops a bit but not much on A/c on.. OR does anything with the ICV actually occur. SLKREd and I did a test with our meters sitting on the windshield and 12v was present at the ICV always so I don't know.

Dan

Last edited by Logon_Bob; 10-26-2008 at 11:13 PM.
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#3 (permalink) Old 10-27-2008, 08:05 AM
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I agree with Dan. Check the continuity of the positive side ICV connector wire (pin 2) going to the OVP relay base pin 87L.

In your case, you could temporarily pull the connector off of the ICV and only attach pin 1 to the ICV, then put a jumper on pin 2 of the ICV to 12v battery. This should put the ICV in a normal operating state, since battery voltage is constantly applied to pin 2 from the OVP relay. Unless someone can prove me wrong, I believe that the ICV operation is controlled on the ground side.

My ICV reads 8.8 ohms across pins 1 & 2. With ignition on from pin 2 to ground I read 12.28v. Across pins 1 & 2, I read 11.51v during normal operation.

*NOTE*- If you pulled the OVP relay out, make sure it is fully seated when you replaced it.





Last edited by slk230red; 10-27-2008 at 08:15 AM.
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#4 (permalink) Old 10-27-2008, 08:40 AM
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Another possible solution for stalling/shaking

I found this during my research, it might be worth reading and checking the passage hole in the breather hose connector. It's on an '87 260E.

"But I still had the following problems

1) Extremely rough, nearly stalling idle after start.
2) Exhaust smells "rich"
3) Hesitation on accelaration from a stop.
4) Intermittent, dramatic loss of power, almost like the fuel was getting restricted to the engine. If I held the accelerator down long enough, it would suddenly kick in and go.
5) Every so often there would be this sound of what sounded like a vacuum release from the engine compartment
6) There would be a rythmic "thunk, thunk, thunk" under certain conditions with the air conditioning on coming from the dashboard.
7)Terrible gas mileage 18 mpg
8) There seems to be a limit to the power of the engine that is artificial and the car will not go any faster than 100 mph, no matter how much gas I give it. I know this isn't scientific, but it "feels" like something is wrong. This started when I put on the silencer.

As I started to pay attention to my vacuum hoses, I noticed that I could make the thunking go away if I gave the car a lot of gas, sometimes. "Hmmm" thinks I. Maybe a vacuum leak, but I could hardly see any hoses. So, off to the junkyard, and I pull off the fuel distributor and air intake components. This way, I don't have to screw up mine and I can find stuff. I find this one hidden hose that was cracked down the seam on all of them at the junkyard. However, it is VERY difficult to get off without removing all the components, so depression sits in once again. The car runs, do I want to screw around with this and risk it not running. So, on my car, I at least push on it a little and see if I can determine if there is a leak in it. Doesn't seem to be.

But, there is this black hose that comes from the valve cover to the air cleaner. Off of this is a sort of cream colored, stiffer plastic hose,about 1/8" OD that connects somewhat loosely to a cylinder that appears to regulate fuel. Such a stupid little connection. But, it's there, so it must do something. The black hose has a little tributary on it where this cream colored hose plugs into. I take my awl and push into it and, "what do you know"...it's clogged...so I push in a little further and clean it out...now it's got a clear path. I put the cream colored hose back on and "voila", problems 1-6 go away, like magic, and the mileage is now a little better. Unbelieveable how easy this was."

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#5 (permalink) Old 10-27-2008, 09:10 AM
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I tried to test resistance of the wire, but I'm not really sure how to work my mulitimeter.

Maybe somebody can help me when I go to test the resistance it starts at a high number and then goes down to a negative number.

For example when I tested the resistance from the OVP to the ICV I got -179ohms

I put in the OVP and tested the pin where the i had coninuity to the ICV and i had 11.51 at the OVP and again 2 volts at the ICV.

Correct me if I am wrong, pin 87L is the one that is supposed to go the ICV. So I should have continuity from this pin to the ICV, right? When tested, it is pin 30 that I have continuity from the OVP to the ICV.

I will go and check out that breather hose from the air cleaner and clean that out. I will also try the direct 12V to the ICV and see how that works.

Also if anyone could with my multimeter I would appreciate.
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#6 (permalink) Old 10-27-2008, 10:00 AM
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First make sure that you have no power applied to your circuitry when using an ohmetere. Next isolate and remove any component you want to measure it's resistance out off the circuit or disconnect from harness.
You measure across a device to get a reading. Oh, make sure your multimeter is set on ohms and that you have the cables in the proper slots. Some meters use different slots for voltage/current and resistance measurements.
Above all make sure you have NO POWER or you WILL fry the instrument.
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#7 (permalink) Old 10-27-2008, 12:07 PM
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More test results and it is starting to get wierd.

What I figured out was I have continuity from pin 30 on the OVP socket to both 1 and 2 on the ICV. This doesn't sound right me, is it? Should there be continuity between pin 30 and pin 1,2(on ICV)

Pin 87L I put a direct 12V to it and when I measured it at the other end, and what do you know only 2.02V.

Since the OVP tested fine I have a feeling that there is no problem with the OVP.

Also, I put a ground and direct 12V to the ICV, and then the the valve moved around inside of the ICV, so I think that it is functional as well. Am I right to assume this?

So there is some wiring problems here aren't there?

So there must be a wiring problem and if you all agree, how am I going to have to start this fix. I am thing that I should make sure there is nothing wrong with the base as Logon_Bob said could be part of the problem.
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#8 (permalink) Old 10-27-2008, 12:11 PM
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Good advice and another issue to find Ohms your meter has a 12v battery installed. When switched to ohms it is applying voltage to the circuit being tested. No big deal checking a wire or for a good ground, but around things like the ECU or maybe even certain parts of the ignition module, you can fry very low voltage circuits. There are special low volt LED testors for such things.

But I think he wants to know what setting to put the meter on,, yes???

If so... you meter has most likely a number of choices under the Ohm section of the meter. Ohms is the upside down "U" thingy.
You might have 2000k, 200k,20k, 2000 and 200 for example. The "k" is 1000

For most of the stuff we are looking at, the lower settings work just find for testing continuity. For just testing a "closed" circuit as you are here testing from one end of the wire to the other end you could choose just about any setting. I prefer something lower, say 2000 or so a copper wire will have little resistance, actually it will show on the meter as no resistance IF not broken. You might try the lowest setting and touch the probe together and actually see their resistance. Might be like 0.09 ,not much but it's there.

Put the meter on say 2000 and simply touch the probe ends together, the meter should start off at "1" then upon touching go to zero or 00.0 This is good idea to do first off anyway to make sure your meter is working. If the "low" battery symbol is flashing, you should first change the battery or you could get a false reading.

For checking this wire, that is what you want to see, 00.0, same as touching the probes together.

Now, for testing the Heater coil on the back end of the ICV. Here you know what you are expecting to see or hopefully anyway somewhere around 12 ohms +- 3, It's a "Known" quantity because a manual or in this case Silkred told you. Different method if you don't know what to expect.

So, what you want to do is set the meter on a max ohms rating just above what you expect to find. So, in this case 200 would be accurate. If you used the next one up, it still should work but YOU have to mentally move the decimal point as shown on the meter. Get's too confusing for me so I always set one click above what I expect to find and it's what you see is what you get.

When you don't know what the rated ohms should be ( good luck here as your shooting in the dark ) but you want to know anyway. If you had a device with say 500 ohms and you had the meter on 200, you should get an error or it may flash and say "1" again.

Increase a click and go again. or start high and work your way down until the error and go back up. Otherwise you have to mentally move the decimal again.

So, let's hope you find the problem. I am no expert here, but I would expect if failed it could fail open circuit ( broken wire inside ) meter will not change and still show "1". IF it fried say a wire coating and is shorted out, I think it would now show infinity or 00.0 on the meter, either way it's bad.

Also, if you get infinity going from the base pin out of the OPV to one of the wires at the connector of the ICV, you might wiggle it bit to see if the connector has a break or intermittent break. It could be the wire is actually broken but making a bit of contact internally until it either gets hot or moved like engine vibrations or something.

Where I fall on my face is, I am suspect of this 2 v's yet you have 12v at the OVP. In my mind the wire could be all but One Strand of wire left and you should still get 12v on the meter,, but, it would not or shouldn't carry enough power ( amps or milliamps ) to run the heater coil. Now this would be straight to the hot wire from the OVP base pin to the hot wire disconnected from the ICV. If your probes were on the OVP pin and the other side of the heater coil, then yes you can experience a voltage drop. Again, anything around a 1 volt drop is bad. But, this should show up with the ohm test of the heater coil.

Enough - And I have my flame suit as I only know enough to be dangerous and subject to correction... :-)

regards
Dan
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#9 (permalink) Old 10-27-2008, 12:24 PM
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Originally Posted by jordanhoff View Post
More test results and it is starting to get wierd.

What I figured out was I have continuity from pin 30 on the OVP socket to both 1 and 2 on the ICV. This doesn't sound right me, is it? Should there be continuity between pin 30 and pin 1,2(on ICV)

***If attached to the ICV, then I would think yes. Your just testing Through the Heater Coil though I would think it should have also shown the 12 or so Ohms just like direct on the heater coil. You just added a length of wire to one end.

Pin 87L I put a direct 12V to it and when I measured it at the other end, and what do you know only 2.02V.

*** ah ha,, that is what I suspected as volts should be equal if even one strand of wire is still attached. I was going to ask HOW you checked the OVP. Looks like you may have the broken or cracked solder joints issue inside the OVP. There are instructions on how and where to resolder them, then check again.

Since the OVP tested fine I have a feeling that there is no problem with the OVP.

Also, I put a ground and direct 12V to the ICV, and then the the valve moved around inside of the ICV, so I think that it is functional as well. Am I right to assume this?

**** sounds good so far. Once you get 12v going to it from the OVP, then do the "ICV Hose Squeeze" test. But, we are assuming if you get the 12v there, all should be good, let's hope.

So there is some wiring problems here aren't there?

So there must be a wiring problem and if you all agree, how am I going to have to start this fix. I am thing that I should make sure there is nothing wrong with the base as Logon_Bob said could be part of the problem.
*** No, you bench tested the OVP and found the issue right. Or wait, are you bench testing or found a way to get at the OVP pin with it installed? This is a good way to check things where you can slightly pull a component out and get to the pin you need, but I found that about impossible with the OVP, it's buried. Where slightly pulling the connector on the ICV while running can be done.

Yippeeee, I think you have found the issue. If you need help to find the How to fix your OVP, pls. advise. I think SLKRed just posted it not too long ago. mmmm Though I think we decided the how to check it the easy way ( not on the bench ) was to check for 12v at the ICV. If not, check the wire, IF not it has to be the OVP. Open it up and resolder the major joints.

Dan
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#10 (permalink) Old 10-27-2008, 12:59 PM
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[QUOTE=jordanhoff;3128101]I tried to test resistance of the wire, but I'm not really sure how to work my mulitimeter.

Maybe somebody can help me when I go to test the resistance it starts at a high number and then goes down to a negative number.

For example when I tested the resistance from the OVP to the ICV I got -179ohms

*** no clue. This is OVP out, pin 87L to disconnected connector ( only one wire ) at the ICV, right? Ohms should be ohms, I dont' think it should be a Negative number. Touch the probe ends together and make sure the meter reads 00.0

I put in the OVP and tested the pin where the i had coninuity to the ICV and i had 11.51 at the OVP and again 2 volts at the ICV.

Correct me if I am wrong, pin 87L is the one that is supposed to go the ICV. So I should have continuity from this pin to the ICV, right? When tested, it is pin 30 that I have continuity from the OVP to the ICV.

*** pin 30 is input from the Postive terminal of the battery. So, with you meter now on Volts, you could check the base plug, pin 30 ( red meter wire ) and the black meter wire to any good ground and you should see 12v's. I assume the key needs to be on run. Wierd thing happen as you don't know if that voltage is going through something or not. IF you were on ohms and were on the positive wire at the ICV and the key was on, then you were running voltage through the meter when set to Ohms, not a good idea like it was told already though some meters have built in protection.

If no continuity between base plug pin 87L and the hot wire at the ICV, then yes you have a break in the circuit as well. Or you may not really be in the correct base pin, easy to do to get turned around.

Dan
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