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 High idle when warm? 
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Joined: Wed Mar 21, 2018 2:51 pm
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Location: Michigan
Post High idle when warm?
I have a 2014 MB 3500 Sport. It only has about 8 hours on it. Everything seems to work just good, except after it has been running for 30 or more minutes the idle does not want to come down below 2000 rpm. After it cools down for 20-30 minutes it will idle between 750 and 800.

Everything on this motor is stock.

Any suggestions?


Wed Apr 25, 2018 7:05 pm
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Post Re: High idle when warm?
when it's ideling high, can you blip the throttle and it goes back to normal idle?


Wed Apr 25, 2018 7:19 pm
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Post Re: High idle when warm?
No. Tried that several times.


Wed Apr 25, 2018 7:54 pm
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MMT F.E.

Joined: Mon Jul 14, 2014 8:19 am
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Post Re: High idle when warm?
Have you adjusted the governed idle spring and the idle speed screw on the front of the motor?


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Wed Apr 25, 2018 9:13 pm
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Post Re: High idle when warm?
I have adjusted the governed idle screw before. But I am not sure where the idle screw on the front is that you're talking about. I will look for that this evening.


Thu Apr 26, 2018 6:08 am
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MMT F.E.

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Post Re: High idle when warm?
It's on the front of the block just behind the cowling. It's adjusts your idle speed.

Undo the two large Phillips screws on the front that remove the smaller triangular piece of the cowling and it's just behind that.

If I was you, I would bend the governed idle spring ran out a hair (towards the muffler so as to ensure that plays no part for now). Warm the engine up, then set the idle on the idle adjustment screw on the front of the engine. Get it to around 1100 rpms out of the water.

Once that is set, bend your governed idle tab back in a hair at a time till it catches and it lifts your idle speed up a hair more (around 1150-1200 so that you now know the governed idle spring will catch properly under load), then just tighten the idle screw another hair. You want the idle adjustment screw and the governed idle tab/spring to both pretty much match the same idle speed of about 1150 so that not under a load your idle speed is at 1150 but you're not constantly bumping off the idle spring to maintain the rpms, but then when you go under load the idle tab/spring kicks in an holds you at approx 850-900 rpms.


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Thu Apr 26, 2018 6:19 am
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Post Re: High idle when warm?
Ok. Sounds easy enough.


Thu Apr 26, 2018 6:28 am
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Post Re: High idle when warm?


Thu Apr 26, 2018 7:15 am
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Post Re: High idle when warm?
Thanks. I appreciate it. I probably won't get a chance to get that deep into it until Saturday or Sunday though.

Getting confused as a real possibility for me. :D


Thu Apr 26, 2018 7:20 am
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Post Re: High idle when warm?
It's easy and takes like 5 mins to warm the engine then 5 mins to complete. Only need a screw driver and needle nose.

Red arrows show where the screws are to remove the cover, green dot is approximately where the idle speed screw is.




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Thu Apr 26, 2018 7:40 am
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Post Re: High idle when warm?
Wow. Thanks. that will help a ton


Thu Apr 26, 2018 8:05 am
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Post Re: High idle when warm?


Bringing this pic back for OP so you know what I am referencing in the PM and previous post.


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Mon Apr 30, 2018 12:47 pm
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