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1984 500sel idle

3205 Views 6 Replies 4 Participants Last post by  48hp
Hello all, I've done a search and now I'm totally confused [:(] I have a 1984 500sel, the idle "stumbles" most of the time when its at op temp, the oil gauge also jumps around while its doing this... thought it was due to rpm dropping then going back to normal but after reading some posts I'm not sure now... something about it being tied into the idle circuit. Anyway it also stalls sometimes when you come to a stop. From what in can figure out I need to clean the air valve and check the elec. box for cracked or cold soldier joints. The elec box is the easy part once I figure out where it is as I've fixed many "junk" Volvo overdrive relays in the past. I guess I'm asking if I'm on the right track and is there anything else I can do?

Thanks in advance for your help:

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48hp - 3/4/2006 1:33 PM

Per Factory Service manual V-8 Engine 116..96 & 117.96:

Checking electric activation of idle spead adjuster (ICV)

Engine - operating temperature.
Ignition switched on.
Pull coupling from idle speed adjuster and measure voltage.

Readout approx. 12v then

Checking regulation of control unit

Engine at idle at operating temp. Plug on couple at idle speed adjuster in a manner that voltage can be measured on plug.

Readout 5v +-1 then

Check idle speed adjuster

Engine at idle.
Simulate coolant temp <42 degree C, for this purpose pull coupling from temp switch and bridge. (located at rear passenger side on top of manifold)

Idle speed increases to approx. 750/min.

End of test

Any other values then those described above suggest a faulty control unit (located at firewall)

If a faulty control unit is found, nowhere within the Mercedes Manual does it suggest this method but others have suggested this and it worked for me. Remove the control unit cover and lightly twisting from side to side while engine is running. Idle should drop to normal speed once twisted in a manner that effects the potential poor solder union. Heat each and every connection, adding a bit of solder to each point. My idle is now on the money.

Hope that helps.
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