Hi,

I have a 1987 560 SL that has been garaged for the past two years. It has 34k mi on it and seems to run fine when driving. However the idle speed appears high. In Park and Neutral, the car idles at around 1500-2000 RPM. In Drive or Reverse at a full stop, it idles at around 1000 RPM. Shifting between these gears at a full stop seems to make the car lurch. Any ideas as to the cause? Thanks.

The engine has an idle/full load contact switch on the throttle butterfly, if that switch doesn't close at idle then the engine will idle at 1000 RPM. You need to have that switch checked out.

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The idle control valve and/or idle control module are common failure points. This 'System' fails safe, that is, the engine goes to high idle upon failure.

Locate the control valve. Test voltage at its' electrical connection, engine warm and running. Should be 5 volts. If not, suspect the idle control module.

If voltage is NOT present, unplug and apply momentary 12volts or constant 5volts to the valve. If idle normalizes the valve is ok. If not, check resistance of valve coil. Should be 4 Ohms, open or very high indicates failed coil in valve - replace. If near 4 Ohms, remove, clean, lube valve and check for hose leaks.

Idle control module (on firewall behind glovebox) is a very common failure. Possible repairs are covered in detail in the Sl section of this forum. This search may help

Thanks to both of you for the advice.

Check the fuse on the OVP relay.