87 560SL Idle is RACING!

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tbase2000 - 21 Mar 2005 07:40 GMT

Help...when I turn the car on the idle is racing high. It use to
start and idle high for a brief second then calm down...now there is
no calming this beast. It?s like I?m stepping on the peddle.

No check engine lights or anything. I?ve looked for broken wires and
hoses but as far as I can tell everything looks good. Could they put
any more hoses and cables in there by the way....

Thanks

Tony

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marlinspike - 21 Mar 2005 16:42 GMT

How high? There are typically two culprits: idle control unit and idle
control valve. If this came on all of a suddent at it's around 1600rpm in
neutral or park, I'd say it's the idle control unit. Not sure where it is on
the SL, probably behind the glovebox.
Richard

> Help...when I turn the car on the idle is racing high. It use to
> start and idle high for a brief second then calm down...now there is
[quoted text clipped - 7 lines]
>
> Tony

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Tiger - 21 Mar 2005 17:26 GMT

I would first start by removing the air cleaner housing and check all vacuum
hoses... make sure they are snug and tight... If you got good ear, you can
hear the suction noise.

IF all hoses are fine, then it is time to check your idle control valve...
it is a cylinder thingy in the front top of engine where there is a
electrical harness on one side and two big hoses on the other side... 90
degree. IF you pull out the electrical harness while the car is idling...
There are two possibilities... if RPM go even higher, it is most likely you
have a vacuum leak somewhere. How high of speed are we talking about?
2000RPM or higher to begin with and go higher from there...

If your RPM is at about 1500, then most likely to be the idle control
computer... which can be obtained reasonably for rebuilt one... check for
vendors at mbcoupes.com under part suppliers.

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