'88 560SL idle too high - PeachParts Mercedes-Benz Forum

DslBnz · #1 06-02-2003, 11:08 AM

THE CAR IS A 1988 560SL
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Upon startup, the car idles at about 1500 rpm. It goes down to about 1000 - 1100 in 'D'. Sounded like the idle control, but it wasn't. Here's what I did:

I replaced the temperature sensor, the ignition control, the air slide, the idle control box, and the K-Jetronic box. These parts were switched out from an '89 560SL. The '89 560SL ran fine with those parts in place, so they were good.

What else should I check? What else would cause this problem? Is the wiring messed up somewhere?

cbdo · #2 06-02-2003, 06:45 PM

The discussion at the site below has to do with 380SL but may offer a few starting points. Certainly the suggestion as to where to look on the service CD will apply. Hope this helps-

http://www.slack.net/~thundt/mercedes/high_idle_hell.htm

DslBnz · #3 06-02-2003, 09:05 PM

Excellent link!

Thanks,

I've already discovered that there is no power getting to the plug connected to the idle speed control.

I will now attempt to change the overvoltage relay as explained on that website.

1991300SEL · #4 06-03-2003, 01:32 AM

Look further down in the following URL - might help:

http://db.mercedes.cx/sec/200302/03/0015.html

VettesRule · #5 08-14-2005, 11:54 AM

Thanks, that was interesting!

sbourg · #6 08-15-2005, 12:05 PM

I didn't look at those threads, but the function of the idle speed valve is to bypass enough air to bring the idle speed up to spec. If idle speed is high with the no voltage to the valve, then the only way the valve could be involved is if it were stuck open - very unlikely. The idle speed control is be doing exactly what you would expect.

Look for a 'vacuum leak', though most likely you will find it as a ruptured larger diameter rubber air supply hose in the idle speed control circuit. If you find such, carefully locate and replace ALL the rubber in the idle airflow circuit, as it will all have hardened and probably break working with it (rather like repairing a problem in galvanized steel house plumbing).

Steve