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Old 01-05-2008, 08:48 PM
Join Date: Dec 2007
Location: chicago
Posts: 53
82 Air/fuel Adjustment Or Idle Adjustment

Heres the ongoing saga. I bought a 82 380sl, had been sitting for around 7 years. Runs good above 1000 rpm, runs rough at 700 rpm.
I've used Seafoam injector cleaner and replaced all the old fuel, idle improved.
I replaced the oxygen sensor, idle improved
Run the car on the expressway, idle improved
added valve and ring cleaner, idle improved
removed and cleaned idle control valve, idle improved
But it is still not correct. At times it seems to surge and miss,, but only at idle.
I removed the air filter and opened the big air intake plate about 1/64th of an inch.(in other words, very slightly) and the idle smoothed out and ran smoothly. I thought I may have found the answer, but I can't find an adjustment for that plate. There is a small metal tube on top of the injector unit that has some spring loaded something inside of it that I had hoped would be able to adjust that plate, but it didn't seem to do anything. Is there some kind of adjustment for that plate to open just a little bit more or how do I get the plate to open. It seems that with the plate open, more air would be let into the injector system. I'm I in the right direction or just guessing at this.

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Old 01-05-2008, 09:44 PM
Join Date: Dec 2007
Location: chicago
Posts: 53
I think I found the answer to part of my own question. After posting the question, I continued to do searches over the internet and found that a 3mm hex wrench in the little hole in the middle of the air filter helped adjust the air/fuel mixture. I don't know if it's perfect, but it idles much better, so I have a great starting point.
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Old 01-06-2008, 01:37 AM
280EZRider's Avatar
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Join Date: Jul 2007
Location: Medford, OR
Posts: 1,477
On the slightly older / different model engines, the adjustment screw is under the air cleaner, which has to taken off to do the adjustment.

I'm currious; did you do this adjustment by ear or with a CO gauge? Because by ear, we don't know if we are leaning the mixture too much.

Don't Chrome them; polish them
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Old 01-06-2008, 07:23 AM
Join Date: Dec 2007
Location: chicago
Posts: 53
You are correct, the adjustment is under the air filter, but is accessible through a small hole in the air cleaner. At least on mine, I didn't have to remove the air cleaner. Yes, I did it my ear for now. I will take it in and have my mechanic fine tune it, but at least I got the idle somewhat smoothed out.
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Old 01-06-2008, 10:24 AM
Registered User
Join Date: Mar 2007
Location: Pine Bluff, Ar.
Posts: 28
Left is Leaner and Right is Richer
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Old 01-10-2008, 08:29 AM
Super Moderator
Join Date: Apr 2000
Location: Falls Church, VA
Posts: 5,316
As has been pointed out numerous times, the correct way to set the mixture on these cars is with a multi meter with a duty cycle. You can find them at Sears for under $30.

There is also technique where you can use the DC voltage setting. Here is a very good article:

It is for the later KE injection, but the principles are the same.

If you find that it needs adjustment it's usually a sign that you need a new oxygen sensor.

Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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