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Old 10-30-2009, 10:58 AM   #1 (permalink)
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Vehicle: 1984 380 SL
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84 380 SL

Ahoy from Dallas Tx

I'm sure there is already a thread on this, as it seems to be a very common problem, but my new old car (84 380SL) has idle problems. Mostly, rough idle and surge at idle. I think I need to check the idle speed relay, but have no clue WHERE it is located on this model.

Also, it had bad tappet noise on the passenger side, so we replaced all rocker arms (was told that the cam was OK) and now after about 500 miles the noise is coming back. Do you think it is the cam?

Finally, has anyone heard of a successful motor swap in this car, putting in an American motor that isn't so exotic?

Dick Brown
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Old 10-30-2009, 11:28 AM   #2 (permalink)
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Originally Posted by sirknightrichard View Post
Ahoy from Dallas Tx

I'm sure there is already a thread on this, as it seems to be a very common problem, but my new old car (84 380SL) has idle problems. Mostly, rough idle and surge at idle. I think I need to check the idle speed relay, but have no clue WHERE it is located on this model.

Also, it had bad tappet noise on the passenger side, so we replaced all rocker arms (was told that the cam was OK) and now after about 500 miles the noise is coming back. Do you think it is the cam?

Finally, has anyone heard of a successful motor swap in this car, putting in an American motor that isn't so exotic?

Dick Brown
Welcome to the wonderful world of the 107.
You can check my thread "my 380SL project" as I have had to deal with the same issues. The engine has cam oiler tubes that run across the top of the cam bearings. I found that mine had some serious blockage that resulted in two of the rockers not getting enough lubrication and going bad. Thus resulting in that wonderful "diesel" sound. Even now when I start her up, it will be noisy for about 30 seconds or so, then it builds enough oil pressure to load the compensators.
Nothing really exotic about the 3.8, it's just a bit different and once you know what to look for it's fairly easily fixed.
Check your vacuum lines and valves for leaks. This is the most common cause of the idle issue. Mine is doing the same thing and I am going to be going through the systems here shortly.
Bandit
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Old 10-30-2009, 03:08 PM   #3 (permalink)
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Old 10-30-2009, 03:11 PM   #4 (permalink)
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Howdy Bandit..

When we replaced the rockers (all of em) on the passenger side, the mechanic noted that the oiler looked "new" and had likely been replaced. In any case, it was clean and functioning properly.

I don't think there is a vaccum leak, either, but I'll try to follow all the hoses and lines and look for a crack or break. I have not found one yet.

From reading threads on the internet (this forum and elsewhere) I tend to think the problem is the idle speed relay, or something in that circuit. I have noticed that the temp guage "jumps" at times (not consistently or frequently, just on occasion) and I am led to believe that the water temp. sensor plays a role in the idle speed relay circuit. However, disconnecting it doesn't seem to make any difference in the "surge" idle. It lopes at idle, but the slightest pressure on the accelerator smooths it out. It's like I need a good old fashioned "idle speed adjustment screw" to turn a few threads!

Later,
Dick
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