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Discussion Starter #1
When the car is stopped in Drive position the engine RPMs go up and down (about 500-700 range). it feels like if you press the accelerator and brake at the same time.<br> <br> The situation is minimized while in Park mode.<br> <br> At the dealer the could not find the problem, they mentionned fuel injectors as a possible source?<br> <br> Any help
 

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Same minor problem. Mine sometimes bounces from 8000 rpm to 5000 rpm, but only when I dont let it warm for 2 or three minutes (and I live in Southern California!) My mech says it's a simple throttle body adjustment, but I have not had time to take it in. Post if you try it and it works.
 

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LOL...you are right...I meant 5000 to about 5800 rpm...Wait...I gonna look.....OK..1000 to about 1800 (What the hell was I thinking? It was that fat joint I just smoked...Such is life on the beach...
 

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Rasputin-<br> You are absolutely right. When I finaly sobered up, I checked it out. I drive the car daily, and it seems to have subsided. Know what I did? Filled her up with 91 octane gasoline and that seems to have cured the problem...Cheap and simple fix!
 

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I have a 1984 380 SL and the RPM goes frequently to 1000 on D. I changed the computer and the Idle control valve ( very expensive ). These two part go together: the computer tells the valve to open when cold. However, the ^problem came back after a year. The idle control valve was a rebuilt, so I may have to change it again. A mechanic told me it could be either the trottle sensor, or the computer ( lots of defects on these )or the cooloing system ( which is new on mine. ) I am trying to get the trottle sensor changed. We have to go by elimination. Charles
 

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Charles,<br> <br> There are numberous factors inducing high idle revs, many of them non-related to the idle valve adjuster or the controller and these are the easier to check first before progressing to series of tests to ascertain whether the adjuster or controller are at fault.<br> <br> Suggest a basic test pertaining the oil temp sensor to eliminate this component from the investigations: run engine to temp and then disconnect the plug from the oil temp thermoswitch and ground it (this connection provides the controller with temp data to increase or decrease voltage to the adjuster). If there is no revs change then this can be eliminated. Then clean the throtle valve (butterfly)and its spindle with carburettor cleaning fluid as carbon deposits causes a partial opening that increases revs. If these to tests fail to reduce revs then suggest to take the adjuster off the car and give an internal cleaning with the cleaning fluid as above several times and finally with DW40 or similara thin oil.<br> <br> On reinstalling the adjuster if not change is noticeable then we can proceed with tests to the OVP and the controller. Let us know results.<br> <br>
 

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Thanks so much for the advice. Now we have a better starting point. I am taking the car in to the garage this week, so will let you know asap.<br> When I phoned the dealer, he said that the trottle switch and/or the mass air flow sensor can be involved. I do not know if the '84 300 SL has a mass air flow sensor. The mechanic should know. what do you think? <br> Charles<br>
 

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Discussion Starter #13
Yes, these can also be the cause, together with a host of other components including rubber hoses, vaccum lines, injectors, timing,spark plugs,OVP, etc, but would not advise replacing components under the so-called 'process of elimination' until they are properly diagnosed faulty.
 

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Cher Rasputin;

It took me a while to give you the results as I had to find a 3rd garage...


Cher Rasputin;

It took me a while to give you the results as I had to find a 3rd garage specialized in electrical problems to get a good diagnose.
Finally, I got the car repaired properly as per your first suggestion. The problem was indeed related to the wire that is connected to the oil temp sensor: the wire was damaged as a bit burned by the manifold. I had also the throttle body and its spindle cleaned.

I sincerely thank you for your sound advice. What a relief.
Are you a mechanic yourseld or " autodidacte "?
If ever you come to province of Quebec,it will be my pleasure to invite you to my place. A la prochaine.
Charles
 

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380 HIGH REVS

Cher Charles,

I am so glad you found the cause of the problem without incurrying high garage costs. (Sorry to have been the causant of depriving the mecs from your hard earned cash![}:)]).

Nope, I am not a mechanic, I just find automotive engineering and electronics a very rewarding hobby and the Rhine barges (Mercs) have been my passion for many, many years (I love my Mercs, but some times I have affairs with my wife![:(!]).

Many thanks for your kind invitation, I do visit Canada on business and I might take you up on that![:D]).
 
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