small problem after cleaning idle control valve. - Mercedes-Benz Forum
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#1 (permalink) Old 09-16-2010, 08:54 AM
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small problem after cleaning idle control valve.

Hello everyone,
I'm from Bethesda, MD and I have a 1990 560SEL with 130,000 miles on it. I have looked at the threads and used search feature. However, after all the helpful advices posted I decided to clean my idle control valve with carb cleaner. Prior to cleaning my idle was 750-800rpm on a warm car and it was shaking i could even see the passenger seat shaking as well, but now after cleaning the idle valve and spraying some carb cleaner on the plate (that goes up and down) the car idles at 950rpm and then goes to 1000rpm and then stays there. The shake went away and the idle is smooth but rpm's a bit high. Once i put it in Drive or reverse rpm's go to normal 600-650 and runs smooth. can you throw some ideas at me? any help would be appreciated.

Than you.
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#2 (permalink) Old 09-16-2010, 11:06 AM
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My car was idling at 1000-1500...So I decided to clean mine...Than after cleaning it still did the same ended up being the wires on the idle control valve hade no connection so I fixed them and now it idles at 500...So if you disconnedt the wire end with the ignition on the on position you will hear a little audible click that means your idel control valve is functioning...So hopefully that helps you some..I am trying to fix my low idle when i cold start it now.
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#3 (permalink) Old 09-16-2010, 03:41 PM
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Thank you for the advice,

The wires are fine since i disconnected the valve while engine was running and rpm went up, i connected it back and rpms went lower. i took the valve out again cleaned it again with carb cleaner checked the 2 elbows that connect to it and then made sure that everything sits tight. started the car and idle was normal again 600-700. However, 20 minutes later I came out and started it again, now when the car was already warm and i let it run for a bit. idle started to idle around 900rpms and doesn't want to go down. what might be the problem.
Thank you.

Last edited by abdimona; 09-16-2010 at 04:05 PM.
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#4 (permalink) Old 09-16-2010, 04:09 PM
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Originally Posted by abdimona View Post
Thank you for the advice,

The wires are fine since i disconnected the valve while engine was running and rpm went up, i connected it back and rpms went lower. i took the valve out again cleaned it again with carb cleaner checked the 2 elbows that connect to it and then made sure that everything sits tight. started the car and idle was normal again 600-700. However, 20 minutes later I came out and started it again, now when the car was already warm and i let it run for a bit. idle started to idle around 900rpms and doesn't want to go down. what might be the problem.
Thank you.
In the meantime make sure to read Benzworld.org - Mercedes-Benz Discussion Forum - Announcements in Forum : W126 S,SE,SEC,SEL,SD,SDL Class
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#5 (permalink) Old 09-16-2010, 05:48 PM
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I had that happen to me. The IAC is nearly 20 years old, so even though I cleaned it to improve it, I think it damaged it slightly, preventing the valve from fully closing when warm. (That's why the idle is high when the engine is at full operating temp... the valve is staying open). That might be what happened to you.

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#6 (permalink) Old 09-16-2010, 07:10 PM
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Well, when I cleaned it the second time i looked inside. the cap on the spring is moving freely. i don't know if it has to be open or closed, when the voltage is not applied, but i moved it up and it closes the valve. also i noticed that the big brass plate (throtle body butterfly) on the intake is not all the way up like it was before. are two of these components related? should i get a used one on ebay? Is there any way to check it? may be i can connect it to a battery 12v and it supposed to be fully closed. I came back 15 minutes ago
and noticed that when i start my car the idle is 600rpms but as the car warms up it raises to 1100rpms
Thanx

Last edited by abdimona; 09-16-2010 at 11:17 PM.
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#7 (permalink) Old 09-17-2010, 01:56 PM
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Quote:
Originally Posted by AGBullit235 View Post
I had that happen to me. The IAC is nearly 20 years old, so even though I cleaned it to improve it, I think it damaged it slightly, preventing the valve from fully closing when warm. (That's why the idle is high when the engine is at full operating temp... the valve is staying open). That might be what happened to you.

I took the valve out and put a plasticancor in it to hold it 1/8" of an inch open. now idle is perfect. I also checked the IAC valve motor. hot engine working parked in neutral. the motor in IAC working but not closing. you were right. thank you. is it worth tobuy it used or better to go with a new?
Thank you

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#8 (permalink) Old 09-18-2010, 12:23 PM
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Ok,guys I give up. I don't know what's going on, but this idle is driving me nuts. Cleanned everything. idle is 1200rpms. replaced vacuume lines. took iac valve and connected it directly to the battery, at 12v closes tight right away. measured the voltage on connector to IAC gives me 4.4-4.8v. Which unit controls the voltage for iac, what else should i look for and where? Please Help

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#9 (permalink) Old 09-18-2010, 12:51 PM
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Cleaning the valve doesn't always work. The contacts inside get pitted over time and can result in an unstable idle. You could try a used one from a wrecking yard but they don't usually warranty electrics. There's an idle control module. That module gets power from the overvoltage protection module. Search the forum for those things and you'll get lots of info as far as location etc.
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#10 (permalink) Old 09-18-2010, 03:55 PM
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Get a smoke test from an indy shop that has a smoke machine. That will show you where the vacuum leak(s) are in the system. You will be surprised !

Cheers,
Gerry
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