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  #1  
Old 03-11-2010, 01:06 PM
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Voltage to ICV?

First, forgive me for starting yet another thread on this topic (high idle), as I'm doing everything i can to prevent taking to shop - while also learning about my car. Have spent weeks studying posts but not sure Im making any progress.

Just installed remfg Idle Control Unit and idle still varies from 800 - 1500 rpms. Seems to idle fine when first started, but rises when it reaches operating temp.
Checked voltage at Idle Control Valve (pulled back connector to reveal pins) and it's reading 0. HOWEVER, if I totally remove conector to ICV, idle surges. Since it surges, wouldnt this mean there is power to ICV? If I disconnect ICU, idle surges. Maybe wiring between ICU and ICV is shorted?
I've put 9v battery to ICV pins and can hear audible click.

I also disconnected oil temp sensor - no change. And vacuum lines seem ok.

I'm stumped again.

Ragtopper
1982 380SL
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  #2  
Old 03-12-2010, 12:17 PM
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It could be the wiring from the idle relay to the valve. That's easy enough to test.

You should also check that the relay has power (pin 2) and ground (pin 4).

The relay gets power from the overvoltage protection relay.
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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #3  
Old 03-12-2010, 12:49 PM
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As always, Thanks Chuck.
If by "relay", you're referring to the Idle Control Unit, it reads 7.3 volts (with key on and probes to receptacles 2 & 4 of ICU harness).
Would this be right?

Ragtopper
1982 380SL
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  #4  
Old 03-12-2010, 02:08 PM
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Correct, relay = ICU.

Those are the correct test points. I just looked in the testing section, and it says and I quote "approx 12v between jacks 2 and 4."

If you want a copy of this section off the CD, send me an email.

Sounds like you have a bad OVP relay or wiring, and the ICU isn't getting enough power to operate.
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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #5  
Old 03-20-2010, 11:08 AM
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update

Bought new OVP relay from MB dealership ($100). Plugged it in and no change. Still idles around 1100 rpms when warm.
Checked new relay and NO voltage to ICU. (fuse good)
Plugged in OLD ovp relay and still feeding 7 volts to ICU.

I guess dealership sold me bad OVP?

Ragtopper
1982 380SL
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  #6  
Old 03-20-2010, 03:22 PM
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What voltage are you getting to the OVP relay? Is there corrosion in the socket?
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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #7  
Old 03-20-2010, 03:27 PM
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Hi Chuck,
Doesnt appear to be any corrosion.
Which receptacles in OVP socket to check?

Ragtopper
1982 380SL
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  #8  
Old 03-20-2010, 03:36 PM
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Just unplugged OVP again, reattached and now getting 10.4 volts to ICU harness.
What gives?

Ragtopper
1982 380SL
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  #9  
Old 03-20-2010, 04:17 PM
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Something flakey in one of the wires or the sockets. Do some shaking and wiggling of wires to see if you can identify it.

If you look at p. 108 of the wiring diagram, the OVP gets its power on on pin 1, big black/red wire from connector c105. That's the big terminal on the right hand inner fender. I think that bad boy is fed directly from the battery.
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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #10  
Old 03-20-2010, 04:37 PM
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Getting 10.7 volts from OVP socket (#1) and same to ICU harness (#2 & 4).
Should be sufficient, eh?
Idles perfect at 550 at startup, but increases to approx 1100 when warm.

Ragtopper
1982 380SL
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  #11  
Old 03-20-2010, 08:41 PM
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My opinion is that that's not enough juice to get the ICU to function right. The spec is 12v. I think you need to find out why the OVP input voltage is low. You should have very close to battery voltage at pin 1.

Suggest y measure your at the big lug on the right fender, then check C105 for corrosion, and test the black/red wire for resistance.
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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #12  
Old 03-21-2010, 02:38 PM
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Chuck, I'm getting 10.7v from main battery, which is consistent w/OVP and ICU.
Time to replace battery?

Ragtopper
1982 380SL
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  #13  
Old 03-21-2010, 03:22 PM
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Either a new battery or maybe a new Volt Meter?
Sounds like you can start the car with no problems so should have close to the needed 12-13 Volts from the battery.
Have someone check calibration on meter.
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  #14  
Old 03-21-2010, 03:52 PM
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What voltage are you seeing across the battery posts with the engine running?
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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #15  
Old 03-22-2010, 01:50 PM
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Getting 12.2 volts with engine running.

Ragtopper
1982 380SL
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