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1988 560SEL
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195 Posts
Discussion Starter #1
Hi Guys,
My 560 starts perfect when its cold, then idles at 600 rpm no problem. Once it heats up the idle creeps up to 1100 and will not go down. It has had the combustion chamber cleaned, idle control valve cleaned, new cap and rotor. Also, when it is hot and you shut if off for 15-20 minutes it will start ok, but runs like it is down one cylinder for about a block or two, until you give it a good boot full of throttle to clear its throat. The mechanic who worked on it today says to get and idle control valve that will solve all the problems, is this the case??? If so, can they be had after market or should i go to the dealer for one??

Thanks,
 

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1991 300 SE
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18,534 Posts
I’m assuming the ICV cleaning did not work and the unit has failed. I’d buy a Bosch valve from one of the online stores, I’ve seen them for less than $200. But the high idle tends to be consistent, hot or cold. Again, it’s possible the valve has partially failed, if you will, and the replacement will solve the problem but you don’t want to throw money at it either. Have you checked for vacuum leaks? It also would not hurt to check the engine temperature sensor. If it’s not working correctly the ECU will instruct the EHA to meter the fuel incorrectly. There may also be a problem with the EHA or throttle valve switch. Each of these components should be checked by your mechanic individually for functionally before recommending the replacement of a given part.
 

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86 420 sel,
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162 Posts
do this quick test: pull the plug off the idler control valve, if the idle rice, then your over volt protection relay is ok. if no change, chk fuse
 

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Depends on the day!
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13,337 Posts
From the sound of things it Could be your air idle valve, but I'm wagering it's a combination of a tired valve and a vacuum leak. When the engine is cold everything rubber is as small as it gets, once things warm up any small leaks tend to get bigger based on my experience.

Have you checked around the injectors w/ some carb clean?? That's a common place as is the air idle valve connection..lastly, I've had the boot underneath the CIS and the plenum seals go bad...

Take a vacuum reading off the back of the intake manifold, should be 16-17lbs STEADY.. If not, you have a leak.

BTW, I sell that valve for 185.

Jonathan
 

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1988 560SEL sold:
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4,717 Posts
[:D]welcome to the high idle club[:D]
[:(]the official W126 V8 owner's club[:(]
[:0]without the high idle experience, your car is not considered initiated[:0]​

do a search in this forum on 'high idle' and you'll get a wealth of information, both struggles and triumphs. It's so easy to throw parts hoping that will be THE PART that fixes the problem. What really helps is the disciplined and analytical approach - perform necessary tests as stipulated in the CD manual, take readings using multimeter etc, and pinpoint the problem before buying parts. Otherwise, you'll end up regarding your car as a money pit.

BTW $185 for the ICV is a good price[:p]

If you happen to change that rubber boot under the CIS, I recommend changing the metal flange that holds the boot as well to ensure proper fit.
 

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1991 300 SE
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18,534 Posts
naomilla - 4/11/2005 11:20 PM

[:D]welcome to the high idle club[:D]
[:(]the official W126 V8 owner's club[:(]
[:0]without the high idle experience, your car is not considered initiated[:0]​
- very good [:D][:D][:D]

Let’s remember that the Bosch K(E) Jetronic fuel injection system was used in all the best European cars during the 70s, 80s, and early 90s. It is a robust and reliable system that can last for well over 200,000 miles and although it can be tough to pinpoint a problem, once the ‘weak link’ is fixed/replaced, the engine runs smooth as silk.
 

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2016 E400 4Matic Sedan
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610 Posts
The ultimate solution for high idle

It took me about 4 months working on the high idle issue. I have done every thing there is on the book, including a trip to the dealer shop ($40) and a certified ICU ($42), without getting any better.

Finally, I went with the ultimate solution - putting a metal plug with a 5 mm hole into the ICV. Sofar, I am very happy with that. The car drives well under all conditions.

The best thing is that I don't ever need to worry about high idle again.
 

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1988 560SEL
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195 Posts
Discussion Starter #8
Wow, well I will try to spend some time this weekend on it. Definetly want to spend the least$ as possible so i will do all the tests. it actually had a head gasket done last year so the vacuum leak may be a starting place. On motorcycles we sprayed wd40 around in controlled amounts and if the idle went up, leak found. I am going to take the idle control valve off myself and soak it in varsol or something to make sure the mechanic did a proper cleaning job. Should it be lubed after? or blown dry and installed?
The idle does race when I unplug the ICV so does that mean its working properly?
Thanks,
 

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86 420 sel,
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162 Posts
IF IDLE GOES UP, IT TELLS ME THAT YOU GET A SIGNAL TO THE VALVE, SO THE OVERLOAD PROTECTION RELAY THAT IS IN THE LOOP WORKS.
LOOK AT A WIRING DIAGRAM IT IS PRETTY STRAIGHT.
 

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Two '87 570SECs, one '87 560SEL
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4,444 Posts
FYI, the ICV should read around 4 ohms if its wiring is intact.

There are LOTS of rubber parts on top of the engine that can leak air, causing the high/rough idle.

Check compression on the engine too, my #8 exhaust valve was cracked and that caused the idle to rise a little and caused a roughness.
 

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1991 560 SEC, 1999 E430, 1989 560 SL, 2002 E430 Sport, 2005 SL500 2005 S500 2008 Gl 320CDI
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172 Posts
Hot start problem is Injector leak down, mine does the same thing. Talked with Ed Owen at Hatch and thats what the problem is. He said it won`t hurt anything.

John
 

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1988 560SEL
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195 Posts
Discussion Starter #12
I thought the injectors might be leaking down but was told no that this system does not suufer from that. How can you tell which injector is leaking? I was going to get it hot then start it let it load the plug up and repeat several times, the leaking cylinder would be obvious then by looking at the plugs and finding the fouled one??? As far as the fast idle, even when it is idling fast it is smooth as silk, it is only rough when started hot and only stays rough for a minute or until you put your foot into it to clean it's throat out.
 

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1988 560SEL
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195 Posts
Discussion Starter #13
Well I guess the next move is to buy an idle control valve as I have checked everything else and nothing helps. I soaked the valve in carb cleaner but it didn't help. I wish I knew someone close to try their valve before I go and order one.
Anybody else have any suggestions?
 

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2016 E400 4Matic Sedan
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610 Posts
elroythekid - 5/15/2005 1:51 PM

Well I guess the next move is to buy an idle control valve as I have checked everything else and nothing helps. I soaked the valve in carb cleaner but it didn't help. I wish I knew someone close to try their valve before I go and order one.
Anybody else have any suggestions?
Hello Kid. The last thing you want to do is to throw parts here w/o knowing what is the root cause of your high idle. Get yourself a decent Digital multi meter and get some readings first. I would do these:

Get the Voltage and amp of ICV and resistance of temp sensors,
Short out the throttle position switch
turn the A/C to max to see if your idle drops

The good news is that after this high idle issue, you would become an experts in MB repair.
 

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Depends on the day!
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13,337 Posts
pull the connection to your ICV, if the idle doensn't move at all your valve isn't working. 9 X out of 10 that's the item I see fail. On a lesser occasion I find the ICU's have failed. Generally, I will see the ICV trying to compensate, so when the connection is pulled the RPM's move right to 1500 and stay there.

You can also put 12 volts to the ICV, see if it will pull the idle Way down.

Jonathan
 

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1988 560SEL
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195 Posts
Discussion Starter #16
I went back out and pulled the ICV off again and let it soak in carb cleaner for 6 hours then re installed it and it idled perfectly for about 2 hours then started moving up again. Not as high as it was but it is back up to 900rpm or so once it warms up. It has to be the valve right?
Also, I had the local shop look at it a couple of weeks ago and they must have pulled the plug on the mixture adjustment screw as it was always plugged. looks like they did it with a chain saw.... How do I re set it? Do I have to take it to the dealer and get it done by them. I'm assuming you need to measure exhaust emissions to adjust??
Thanks.
 

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1991 420sel
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267 Posts
Elroy--What you have described is a classic ICV failure. To be sure, (i) make sure the idle position switch is working, (ii) make sure the B11/2 temp senders are working, (iii) measure the current throught the ICV, and (iv) check for vacuum leaks. A simple DVOM is all you need for tests i-iii. If there are no vacuum leaks, the current through the ICV should be 1000MA. If it is, then what is happening is that the ICV is sticky, and not fully responding to the idle control relay. The ICV can test fine (resistance and clicking when voltage applied) and still not work right. Cleaning it sometimes makes it work, but I have also experienced these being "fixed" for only a few hours. Do not lubricate after cleaning. A new one is only around $185, and aftermarket VDO is the same as MB. Hack mechanics may try to lower idle by leaning out the mixture screw. You can reset this with a simple DVOM and a 3mm hex key. Set the mixture so that current through the EHA hovers around 0, and the voltage (using simple voltmeter) between pins 2 and 3 of X-11 diagnostic socket occilates between 5.7 and 7.5 volts. Setting the mixture control with an ordinary DVOM is described in 2 articles -- one by steve brotherton (on the web) and the other on the www.landiss.com/mixture.htm website. Dont even try it without reading and understnding these 2 articles and the relevant portions of the manual. But the "lambda on-off ratio tester" is really a $5 voltmeter, and that is all you need to set the mixture. Charlie Wagner, 1989 and 1991 420sels
 

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1988 560SEL
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195 Posts
Discussion Starter #18
Thanks Charlie, A few questions, probably stupid, I know I should know this but..

What is VDO and where is it?
What is EHA and where is it?

I am going to go get the two articles later toaday of the web, I'm away until Monday but will try this next week.
Thanks again you guys rock.
 

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1988 560SEL
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195 Posts
Discussion Starter #19
Thanks Charlie, A few questions, probably stupid, I know I should know this but..

What is VDO and where is it?
What is EHA and where is it?

I am going to go get the two articles later today of the web, I'm away until Monday but will try this next week.
Thanks again you guys rock.
 
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