500 SEC Engine Swap, High Idle; Where do I start? - Mercedes-Benz Forum
 
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post #1 of 10 (permalink) Old 06-08-2019, 09:30 PM Thread Starter
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Question 500 SEC Engine Swap, High Idle; Where do I start?

I swapped out my single row timing chain 380 engine for a 500 SEC engine and started it for the first time today. Played around with the timing and when it runs the best it idles at about 1500 RPM. What should I check first to find out why the idle is so high. I'll post a thread on the engine swap once I have it on the road.
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post #2 of 10 (permalink) Old 06-08-2019, 11:40 PM
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The idle air valve has an electrical connection. When I unplug it, my idle goes to 1500 rpm.

Maybe try the idle air valve don your 380 motor and see what happens.


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post #3 of 10 (permalink) Old 06-09-2019, 07:41 PM Thread Starter
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The idle air valve has an electrical connection. When I unplug it, my idle goes to 1500 rpm.

Maybe try the idle air valve don your 380 motor and see what happens.


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That didn't work but thanks for suggesting it.
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post #4 of 10 (permalink) Old 06-09-2019, 11:48 PM
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a vacume leak will do the same thing depending on how bad it is..check everything and if you dont find anything you can start spraying the leak possible areas with carb cleaner..depending on the type the idle will go up or down when you get close to a spot
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post #5 of 10 (permalink) Old 06-10-2019, 05:36 PM
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a vacume leak will do the same thing depending on how bad it is..check everything and if you dont find anything you can start spraying the leak possible areas with carb cleaner..depending on the type the idle will go up or down when you get close to a spot
Vacuum leak or "false air".

You can also use a plumber's torch (don't light it!!!) and see if the propane increases the idle.

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post #6 of 10 (permalink) Old 06-10-2019, 06:47 PM
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500 SEC Engine Swap, High Idle; Where do I start?

Does disconnecting the wire to the idle control valve do ANYTHING to the idle speed? If not, I wonder if you have a wide open idle control valve.

If it sounds like the idle control valve is not doing its job, then hereís a thread I recently started to try and track down how the idle control valve works. The YouTube video in the thread is very helpful in my opinion.

https://www.benzworld.org/forums/r-c...topics/3028292




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post #7 of 10 (permalink) Old 06-10-2019, 10:39 PM Thread Starter
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Vacuum leak or "false air".

You can also use a plumber's torch (don't light it!!!) and see if the propane increases the idle.
I have both so I will check it this weekend. Wish I had access to a smoke machine. I will also study the videos Fonzi posted about. It runs and runs smooth so I'm happy about that. I'm confident that I can get the idle sorted out before the SoCal GTG.
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post #8 of 10 (permalink) Old 06-10-2019, 10:41 PM Thread Starter
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Does disconnecting the wire to the idle control valve do ANYTHING to the idle speed? If not, I wonder if you have a wide open idle control valve.

If it sounds like the idle control valve is not doing its job, then hereís a thread I recently started to try and track down how the idle control valve works. The YouTube video in the thread is very helpful in my opinion.

https://www.benzworld.org/forums/r-c...topics/3028292




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I watched the one you posted and will watch the others. I'm sure I will find the problem. Thanks!!!
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post #9 of 10 (permalink) Old 06-15-2019, 04:38 PM Thread Starter
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Got out a can of carb cleaner to check for leaks. Found I had a cracked, leaking check valve. I checked voltage at the Idle control valve while running and get 3.7 volts. Adjusted the timing and idle is now around 900. I can live with that. Now I just have to finish buttoning it up and I'll be ready to take it for a ride tomorrow.
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post #10 of 10 (permalink) Old 06-15-2019, 09:02 PM
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Ah, yes. Welcome to High Idle Hell. I was there for a while back in 2012 but I finally fixed it.

If you do a google search for "high idle hell" with the quotation marks it'll find a number of forum posts with that exact title.

https://www.benzworld.org/forums/r-c...le-causes.html

High Idle Hell - PeachParts Mercedes-Benz Forum

And even some entries with that title on YouTube:

Good luck. At some point you will find a way out of High Idle Hell, a place where many have dwelt and there is plenty of information from others who've escaped.

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