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Old 10-24-2005, 06:09 PM
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Join Date: Sep 2005
Posts: 8
idle speed too fast ~1700-1800 RPM 1988 420SEL

idle speed too high ~1800RPM [excerpted from MB DIAG. CD-ROM]
check overprotection relay, fuse on relay may be blown or relay defective, air/fuel mixture too lean. oxygen sensor shorted to ground, check wiring between CIS-E control unit and EHA/Electro-Hydrauilic Actuator; EHA current should be ~75mA

turned out to be that the overprotection relay was blown
started up like a champ after replacing fuse. idles cold at about 850RPM manual says should be around 650 when warmed up.
but after the engine got hot was back up tp 1500 RPM what gives ?? adjusting fuel/air mixture made no difference either.
if i jumped on accelerator jumped down to 900 then worked its way back up again , in gear drops down closer to where it should be manual says idle is supposed to be 650 but is around 800 in gear.

Last edited by william.wood; 10-24-2005 at 06:21 PM. Reason: more facts
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Old 05-05-2006, 04:59 PM
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Join Date: May 2006
Posts: 4
Unhappy Idle at 3000 rpm always

I have a 1983 380 (upgraded to a 560 outside) that idles at 3000 rpms. I have replaced the idle control valve and the idle control unit and it still idles at 3000 rpms in adition it now has started dieing at stop lights after it lurches and acts as if it is gas starved. Where should I look next sensors? feul filter? vacuum lines? Is stevebfl out there?
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Old 05-05-2006, 08:09 PM
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Join Date: Mar 2003
Location: Southern California
Posts: 2,161
Check that the TVS closes at idle. No TVS idle signal, no idle speed control.

PS Don't confuse TVS with the microswitch on the linkage - two different aninmals. The TVS is at the end of the throttle valve shaft. It should have three wires - idle, WOT, and ground. Trace the TVS pigtail to the engine harness connector, and run your contintuity checks there.

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Old 05-23-2006, 03:50 PM
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Join Date: May 2006
Posts: 4
Testing Idle Control Valve

I have checked the wires going to the idle control valve and it reads 12 volts. This would indicate that the idle control valve is faulty, correct? As a new valve is over $200 I would like to make sure that it is, in fact, bad before replacing it. Is there any way to determine if it is bad (bench test)?
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Old 05-23-2006, 06:41 PM
GVB GVB is offline
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Join Date: May 2006
Posts: 178
You have to check the current to the air valve. In Amps or mA. Like a drain on a 12 volt system, you hook a volt meeter to and it will say 12 volts, but what you have to check is the amps.
Sounds like you have vacuum issues if you did what the previouse post said to do.

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