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1989 500 SEC, Arctic White (147)/Sato Grey (7738) - Dark Blue Leather (262)
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124 Posts
Discussion Starter #1
OK, my high idle problem has now got so bad that the car never idles lower than about 1100rpm in park. I pulled the electrical connection off the Idle Control Valve (idle increased to about 1500) and put a meter on the two pins sticking out of the back of the valve. Reading of 4.4 Ohms was the result.

How does this reading seem to those who know about such things? I've read that it should be closer to 10 Ohms? Does a reading of 4.4 mean the valve is knackered?

J.
 

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1989 500 SEC, Arctic White (147)/Sato Grey (7738) - Dark Blue Leather (262)
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124 Posts
Discussion Starter #3
Nope, sorry. Most of that went straight over my head. I did try pulling the connections off the temperature senders - no change.

J.
 

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1993 300TE, 1995 E320 Wagon
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1,895 Posts
High idle partial solution

I've been going through this same issue (my idle was around 1100 as well). I first checked the voltage at the ICV (it should be about 4-5 V). This was normal on my car, so then what? One check that was suggested was to attach one of the two pins on the ICV to ground, and the other to 12V (very briefly). If the engine speed drops significantly (or stalls), then the ICV is probably OK (as in, no sticking). Mine passed this test fine, so I went further into things. I also checked the resistance between poles on the temperature sensor (mine is the four-pin type, and resistance is measured between diagonal pins). Mine turned up normal readings (I can't remember what they were, but they can be found in the manuals). I've replaced the OVP relay (nothing changed), the idle control unit (my old one worked better than the "new" replacement?!?), and I've also checked the vacuum off of the back of the intake manifold (steady at about 19 psi). The only thing that has had an effect was to replace the air supply hoses leading to/from the ICV. My PO had replaced the distribution hoses lying next to the valve covers, but not the thicker ones that supply them. I also replaced the air return hose from the left (driver's) valve cover, and cleaned up the cold start valve at the same time (everything listed above is attached to the same point). Easy to do and about $50 total from AutohausAZ, as I recall. My idle dropped to about 850 in park/neutral, which is still not ideal, but progress. Given that this fixed a leak in the air supply that didn't show up as a vacuum leak, my next guess would be to replace the plenum/boot and the "donuts" beneath the fuel distributor, but that's significantly deeper surgery, and I'm not quite ready to do that. Hope this gives you some ideas!

I also purchased a second ICV (not new, but works just as well as my original) that I could sell you if you decide to replace yours...
 

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1989 500 SEC, Arctic White (147)/Sato Grey (7738) - Dark Blue Leather (262)
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124 Posts
Discussion Starter #5
ElRojo said:
I also purchased a second ICV (not new, but works just as well as my original) that I could sell you if you decide to replace yours...
Do you know what resistance it is showing?

J.
 

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1991 420 SEL
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52 Posts
I gave up after I went through all the checklists that the previous poster mentions and didnt find anything wrong. Finally, decided to put a garden hose valve into the ICV intake tube and that fixed the issue. I have it for sometime now and the idle is 600-650 at park/neutral and 500 at drive. I dont even hear engine noise when i am at stop light. So far loving it.
 

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1991 420sel
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267 Posts
The resistance of the ICV (unplugged) should be about 4.5 ohms, IIRC. It should respond to the "click test" per the manual--momentarily touch the contacts of a 9-volt battery to the ICV prongs, and you should hear a click noise. (Note that passing these tests still doesnt mean the ICV is fully operational, however, as it could be sticky. And dont leave the battery connected for more than a moment.) Then reconnect the ICV leads, but dont put them on fully, and with the engine running at idle, measure the voltage between the 2 ICV prongs (be careful not to short the terminals). It sound be about 5.5 volts. Then hook an ammeter in series into the ICV circuit (you will need to make up some sort of wire harness for this), and measure the currrent going through the ICV at idle. If it is 1000ma, then the idle control relay is working as hard as it can to keep the idle down, and the problem is either the ICV sticking or vacuum leaks. If the current is less than 1000ma, and/or the voltage is low, then the problem is in the idle switch, the idle control relay, the B-11/2 temp senders, the wiring or one of the other inputs to the idle control system. The manual has the tests all laid out, and testing the idle switch and the temp senders is easy, needing only resistance measurements. If you have the 1000ma max current at the ICV, but you still have a high idle (this is the situation at least 50% of the time in the later cars), either the ICV is sticky or you have vacuum leaks. You can try to clean the ICV with carb cleaner (do not oil it after cleaning), but in my experience, they go after about 120Kmi and need to be replaced. Fairly cheap in aftermarket. Very expensive from MB.
BTW, the foregoing is form my experience on US 420/560 cars, and your euro 500 may be slightly different. Charlie
 

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1993 300TE, 1995 E320 Wagon
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Quote:
Originally Posted by ElRojo

I also purchased a second ICV (not new, but works just as well as my original) that I could sell you if you decide to replace yours...

Do you know what resistance it is showing?

J.

I'll check when I get home on Monday-- I'm away on business.

Dave
 

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1982 Euro 500SEL
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82 Euro 500SEL High Idle

Teutone,
Thanks very much for your 2007 post with the pdf of the test procedures for idle problems.

The name plate data for my 82 Euro 500SEL carries SN WDB12603712016005 and indicataes a 117 engine number. The test procedure appears to address only the 116 engine for model years 81 and 82.

Your posts certainly place you among the ranks of the "knowledgeable". In your experience are there likely to be enough differences between a 116 and a 117 engine to warrant concern when trying to run a high idle problem to ground?

My idle problem is intermittent. I have replaced the ICU and the ICV with scrap yard scavenged units. The 2nd used unit from an 85 Euro 500SEL with a 117 engine has, at least, changed the idle characteristics. With hot engine the idle will drop to 500rpm some of the time (when demon is behaving). The rest of the time the idle runs up to 1500 unloaded (900 +/- in gear).

I have tapped the ICU and physically twisted the board without any changes in idle speed. The ICU responds (loud click) to a momentary 12v input. 3 to 4 seconds applic of supplemental 12v input kills the engine. The test procedure indicates a bad ICV for this condition. Intuitively this doesn't sound right.

I realize what I have done to date is not procedurally sequential testing, but do you have any thoughts with the available data before I dive into the engine room for the full test sequence?

As a last novice question in order to bring the idle down does the ICV increase or decrease air flow into the tubular black ducts that feed the air intake system above the throttle body? When the air flow butterfly opens with throttle increase does the ICU shut the ICV down or set it to full open?

Thank you very much for your help and the sound advice you have given out in your 10,000+ posts.

Regards,

JR
 

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CH4S Admin , Outstanding Contributor
1985 500SEC, 1991 190E 2.6.
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42,211 Posts
Not so, the file applies to the M116, and M117.
Here is the header:
07 Mechanical/Electronic Injection - M116/3.8 L & M117/5.0 L
 

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1982 Euro 500SEL
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500SEL High Idle

Teutone,

Thank you for the response. Dumb question on the part of this novice. I didn't do enough research to realize the 116 nomenclature is the 3.8L engine.

I'll go into the test procedure full bore.

Regards,

JR
 

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1990 Mercedes 560SEL
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313 Posts
Let us know what your findings are.

I've got high idle again after replacing the fuel distributor. I'm thinking it could be a bad seal, but I haven't had time to investigate, and it sounds like your on a very strong track.

Good luck.
 

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'87 560SEC: '86 AMG 560SEC: '87 560SEL - PAST: Heckflosse 190 & 230S
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1,479 Posts
Hi Idle

560sec in the shop (finally), ostensibly to diagnose hi-idle in P/hard shift in R & lifter noise.

Indy 1st ran smoke test and I guess it leaks like a sieve :eek:
His approach is to tackle vacuum leaks ID'd (injector seals, etc.), before trying to pinpoint the high-idle pbm, which in-turn is exacerbating the shifting issue. He did mention a bad throttle valve switch as a potential culprit.

Don't know if this info adds value, or is just FUD at this point... but will try to update this thread once prognosis is official.

On a different note: I picked up this SEC with zero history/receipts, so when I brought it in, he also told me he'd render an opinion as to whether the car was worth even dropping $$'s into. After reading here... I was fearing the passenger-side cam as the source of the 'knock'.

However once he pulled the cover - he said it was amazingly clean and @ 200k, obviously well-cared for. Except that the chain guides looked ORIGINAL & were just about to go!!! Needless to say chain/rails, etc. are getting done now, but between:
  • catching the chain JIT,
  • a glowing report from a factory-trained guy whose owned SEC's himself, and,
  • a purchase price of $2K

At the moment, things are looking pretty positive ! Tho between tranny work, exhaust system, rust repairs/rear-window seals, and paint - not to mention the yet unforeseen gremlins, yada-yada... it may be a loooong time before I can think about decent rims :D
 

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1990 Mercedes 560SEL
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Well my idle was fine before I replaced my fuel distributor.

I replaced all of the injector rubber, air idle hoses, intake boot, throttle position switch, etc etc. and my idle finally got down to about 650.

But as soon as I replaced my fuel distributor, it jumped back up to 1100. It's frustrating because I'm not able to find a vacuum leak, unless of course it's coming from the fuel distributor seal itself.
 

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'87 560SEC: '86 AMG 560SEC: '87 560SEL - PAST: Heckflosse 190 & 230S
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1,479 Posts
High Idle (upd.)

Well in my case, turns out I need a Idle Air/Speed Control Valve. It even sounds like an obvious candidate :rolleyes:

The Indy (RDM Imports in Tiverton RI) loaned me his test unit, until I get a new one ordered. How standup is that ? :thumbsup:

Vacuum/idle corrections did a lot to ease the hard engage going into reverse, but it's clear that tranny specific R&R will necessary. It's just part of a long repair to-do list he gave me.

While the spirit is willing... the wallet is weak. Oh well, the SEL prolly makes for a better snow-sled anyway. MUSH!
 

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1991 560 SEC 1994 E500 2014 E350 Cab
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7,028 Posts
Mine is currently getting an overhaul for high idle. Since my compression was still at 149 PSI in all 8 cyls, I went ahead with RR all vac lines, rubber connectors, injectors seals seats etc. If it touches the intake manifold, it is getting replaced. New plugs wires rotar and cap, hoses. Mine hit P idle of 1100 and slammed into R, and the other day it stopped slamming. I was happy until I didn't move in Reverse. LOL Rebuilding tranny, but needed to find reason for High Idle. ICV was spec, but smoke test revealed multiple manifold leaks and several failures of vac lines and rotted rubber.

Seems previous owner relied on his shop to adjust air mixture to avoid stalls in gear, rather than to properly diagnose the issues. Too bad I got the ultimate bill but she is worth it. I get it back Tuesday!
 
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