380SL Rough idle unidentified wire and vacuum hoses - Mercedes-Benz Forum
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post #1 of 4 Old 05-29-2008, 05:46 PM Thread Starter
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Unhappy 380SL Rough idle unidentified wire and vacuum hoses

Being he nice bother that I am, I graciously offered to help my brother with his 1984 380SL. One of his timing guides broke, his chain jumped a link and you know the rest of the story.

I’ve worked on many American and Jap cars before, but this is my first time tearing into a Mercedes. During my spare time and a few months later, I now know why the shop wanted 4-6K for the job.

I labeled most of the wires but was unable to take pics at the time I was tearing it apart. I found a wire and vacuum diagram at the library, but it does not illustrate the parts I’m searching for.

Once I got it all back together, it did start up only after a few quick cranks, however, it is running very rough and will not idle. I adjusted the timing and little improvement. During reassembly, I replaced all belt and hoses including vacuum hoses and fittings. I believe I got the valve timing correct during reassembly. I’ve disconnected the Idle Speed Adjuster (electrical connection) and this made no difference. The adjuster appears to be in working order, as the valve opens and closes. My brother said it ran great the day before the vales smashed. It’s been sitting about 7-8 months. Today I’m draining the tank, checking the fuel filter and will try some premium gas with fuel cleaner.

I do have a few questions regarding some wires and hoses I’m uncertain about and hoping someone can help with. I’m not sure if they are related on not but here goes:

I’m rather certain I got all the wire connections correct with once exception. On the top right side coming form the main wire harness, there is a single orange wire with an eye and bold connection. I have no Idea where this goes. Any ideas? See attached pic.

As I mentioned, I found an emissions diagram for the vehicle, so I’m certain most of the hoses are correctly hooked up. However, there are a few not illustrated:

There appears to be a fitting coming from the top of the Warm Up Compensator. The white hoses on the side are hooked up and in my diagram, but here is what appears to be a hose connection on the top. I ran this to what I believe is the ‘Kick Down’ switch located the right wheel well next to the radiator filler bottle. Can anyone confirm these two hook together?

One additional hose I’m uncertain about is one that runs from a tee located toward the back bottom of the fuel distributor. One end hooks into some sort of valve that has fuel hoses running into the distributor. The other end I ran into the breather tube from the valve cover.

I’ve attached some pics. Hope someone can point me in the right direction of give some useful suggestions on what to try, or if anyone knows of a reliable Mercedes Mechanic in the Las Vegas area, I’m getting close to taking it in.

Thanks in advance.

Update - later that day....

I drained the, checked the filter and all looked good. I put in some premium with some fuel cleaner.

I read a post earlier that talking about cleaning the Idle Speed Adjuster with some carb cleaner. I did that and when I disconnected, idle did increase, but still no power.

For grins, I connected the orange wire to ground and that did something! It activated an electric valve hooked into the fuel distributor mounted horizontally on the left side. Not sure what it is, but it did wonders.

Question, is this suppose to be hooked to ground, or is there a particular place?

Thanks again - by the way, great fourm.
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Last edited by cjmarinch; 05-29-2008 at 11:38 PM.
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post #2 of 4 Old 06-27-2008, 06:06 PM
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the wire bolts to the bracket that is bolted down to the thermostat housing. can't remember the hose, but I'll try to look tomorrow
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post #3 of 4 Old 08-15-2008, 08:56 PM
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I have the MBZ fac manuals for 380SE (116 engine, 126 body).

with respect to the black tube you connected to the compensator:

The bent hose on the top of the compensator is a vent to the inside of the box. leave it open. the box is solely to enrich the mixture during cold operation and during accel during cold operation. the vacuum connections to the box are for mixture enrichment during cold (< 50 C) accel. the electrical on top is to an internal bimetal strip that provides enrichment during intial warm-up. right next to the box is a thermo vacuum switch. above 50C this kills the vacuum circuit to the one half of the internal diaphragm to disable accel enrichment with a warm engine. when cold the control pressure should be say 1.5 - 2 bar. when warm, the pressure should be say 3.5 bar.

altho you do not show it, i suspect that black tub is the vacuum source line that runs from the intake manifold close to the fuel distributor to the compensator port closest to the fuel distributor. the other port on the compensator goes to a restrictor in the manifold vacuum line. the restrictor is what enables a brief enrichment during cold accel.

if you read this far and need more, drop me a line (mumtaj@earthlink.net)

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post #4 of 4 Old 10-11-2010, 04:08 PM
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Similiar problem

Hi, newbie here, recently obtained a very nice 380sl, 1985 and it has steadly gotten worse and worse at idle. At first it ran pretty good and had about 3/4 tank of gas. After about 100 mile it began to develope a very rich and rough idle intermittently. Happened after being turned off after reaching normal temp and restarted after a short time. The idle control valve is not energizing and have found what appears to be and open wire from the control unit. Have no wiring diagram to see it there is any thing between the valve connector and controller plug. really appreciate any hints.
Thanks, DW
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