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  #1  
Old 09-22-2012, 04:06 PM
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Join Date: Feb 2003
Location: Oklahoma
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Help with Codes 18, 28 & 31 - '91 300CE

My '91 300CE (M104) has 86K and I am having ongoing trouble with starting and mpg issues...

Duty cycle start at 70% with KOEO and 50% at idle - once car warms up, the cycle drops to 1-5% and stays there until I rev motor...climbs back to 50% and then upon resuming idle drops back and hovers from 1-5%.

Why is this happening?

I pulled 3 codes - Code 18 = "Current to idle control valve is illogical", Codes 28 and 31 = "Intermittent contact in engine coolant temperature sensor circuit..."

I just replaced the 4 prong engine coolant temp sensor a couple of months ago (and, Yes, I reset the codes before pulling these codes this morning...)

Any ideas? I am and have been at a loss to figure this out and I can't find anyone local that has been of much help!

Thanks, ryan

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RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE
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  #2  
Old 09-22-2012, 08:06 PM
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Location: Los Angeles, CA
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how does your wiring harness look
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Old 09-22-2012, 08:33 PM
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Join Date: Feb 2003
Location: Oklahoma
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My understanding is that the '91 model W124's didn't have the wiring harness problem - and as far as I can tell, things look fine, although I'm not exactly sure what I'm looking for...

ryan
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RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE
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  #4  
Old 09-27-2012, 09:41 AM
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Join Date: Apr 2000
Location: Falls Church, VA
Posts: 5,318
Suggest you check the continuity from the coolant sensor to the connectors at the ECU. With your meter hooked, up, jiggle the wiring and see if the readings change.

You can check the wiring harness by slitting the vinyl jacket or taping in various places (especially where it's likely to get hot) and looking for crumbling insulation on the wires.

You might have a bad EHA and the ECU is saying "Under these conditions I shouldn't have to be sending this much current to the EHA to control the mixture."

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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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