380sl high idle and running hot - Mercedes-Benz Forum
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post #1 of 100 (permalink) Old 08-22-2018, 08:15 AM Thread Starter
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380sl high idle and running hot

I'm searching for the reason I have zero volts at the idle control valve (idles at 1200 -1300rpm) but while checking I noticed that the temp was running hot... about 90c. With the engine off but still hot I could easily turn the fan... almost no resistance. So I replaced the fan clutch and ran the engine to full temp again... no difference, the gauge still went up to 90c (maybe a little higher) and stayed there.

The engine starts out running extremely rich... you can smell it in the exhaust... but after it warms up it runs pretty good except for the high idle.

Here's a video shot this morning of the engine running after it warmed up.

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post #2 of 100 (permalink) Old 08-22-2018, 02:19 PM
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Bear with me here.....What controls the ICV?

Signal / voltage from where?

Is there a temp sensor somewhere?

It must be getting a "I'm warmed up now" signal from something.

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post #3 of 100 (permalink) Old 08-22-2018, 04:04 PM Thread Starter
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@nobby I traced down the source of the problem.

The idle control unit sends a signal (around 5 volts but varying) to the idle control valve via pins 3 & 5 on the idle control unit. I measured zero volts on pins 3 & 5 on the icu. Next I checked the voltage getting into the icu... it gets it's voltage (on pins 2 & 4) from the over voltage protection relay. I removed the over voltage protection relay and mocked up the circuit on my bench. I supplied 12 volts to the relay actuator pins and I could hear the relay close. I then put an ohmmeter across the two pins the relay is supposed to connect when closed and activated the relay... there was no continuity and therefore no voltage to the icu. The 10 amp fuse on top of the relay housing is good, so the only other thing it can be is an open connection inside the over voltage protection relay.

I ordered a new over voltage protection relay from AutohausAZ and threw in an order for a fuel pump relay as well. May as well keep one of those handy for when my 34 year old fuel pump relay goes bad on my way the SC in October.
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post #4 of 100 (permalink) Old 08-22-2018, 08:19 PM
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@nobby I traced down the source of the problem.

The idle control unit sends a signal (around 5 volts but varying) to the idle control valve via pins 3 & 5 on the idle control unit. I measured zero volts on pins 3 & 5 on the icu. Next I checked the voltage getting into the icu... it gets it's voltage (on pins 2 & 4) from the over voltage protection relay. I removed the over voltage protection relay and mocked up the circuit on my bench. I supplied 12 volts to the relay actuator pins and I could hear the relay close. I then put an ohmmeter across the two pins the relay is supposed to connect when closed and activated the relay... there was no continuity and therefore no voltage to the icu. The 10 amp fuse on top of the relay housing is good, so the only other thing it can be is an open connection inside the over voltage protection relay.

I ordered a new over voltage protection relay from AutohausAZ and threw in an order for a fuel pump relay as well. May as well keep one of those handy for when my 34 year old fuel pump relay goes bad on my way the SC in October.
Good wrenching!

I find myself looking forward to the "What's Jyuma Up To Today?" show.
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post #5 of 100 (permalink) Old 08-22-2018, 09:29 PM Thread Starter
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Good wrenching!

I find myself looking forward to the "What's Jyuma Up To Today?" show.
My wife often asks that very question... "What the hell are you up to today"? I don't think she finds it entertaining.

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post #6 of 100 (permalink) Old 08-23-2018, 04:00 AM
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Good wrenching!

I find myself looking forward to the "What's Jyuma Up To Today?" show.
Me too.
He's got a 380SL similar to mine and seems to be doing a meticulous job restoring components. Gonna be a nice vehicle when he's done ... well, we never get done with these do we?
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"You have chosen to drive a MERCEDES-BENZ, a car in whose construction and production we have taken great pains because we believe that quality is not a matter of chance." -- page 3, Owners Manual 380SL
Timing Chain, Subframe, wiring harness, Climate Control, Rust prevention, etc.
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post #7 of 100 (permalink) Old 08-23-2018, 05:58 AM
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Me too.
He's got a 380SL similar to mine and seems to be doing a meticulous job restoring components. Gonna be a nice vehicle when he's done ... well, we never get done with these do we?
You're never done with a 107. All you can do is declare victory and enjoy the car.

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post #8 of 100 (permalink) Old 08-23-2018, 08:59 AM Thread Starter
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Quick... somebody check the temperature in hell. I ordered two relays from AutohausAZ yesterday afternoon and they were delivered today before noon?

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post #9 of 100 (permalink) Old 08-23-2018, 11:22 AM
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Quick... somebody check the temperature in hell. I ordered two relays from AutohausAZ yesterday afternoon and they were delivered today before noon?
They must be following all your threads.

The sooner you get these relays installed.....the sooner you find the NEXT problem.

And.....order more parts.

Quote:
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Donítí ever wrestle with a pig. Youíll both get dirty, but the pig will enjoy it.
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Soldier on Old Chap. The Pig is you and you are the Pig.




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post #10 of 100 (permalink) Old 08-23-2018, 12:55 PM Thread Starter
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They must be following all your threads.

The sooner you get these relays installed.....the sooner you find the NEXT problem.

And.....order more parts.
You may be right... I already found my next problem.

I installed the over voltage protection relay and immediately my high idle problem was gone. Now I have 3 new problems...
1... my idle is now way too low... under 500 rpm.
2... lifter tick is back with a vengeance.
3... Engine is chugging like it's running on 7 cylinders.

If I rev the engine the lifter noise goes away so I'm assuming I have a hydraulic compensator someplace that can't retain the oil pressure at low rpm (and therefore lower oil pressure) or I'm running into that 5.1 versus 5.35 thrust washer problem. Here's the strange part... I ordered the thrust washers on 8/18 and my order review on the autohaus website says delivery will take another week. Almost 2 weeks to get thrust washers and overnight to get 2 relay's. Go figure.

I'll take a video of the engine running so maybe someone might have their memory jogged and say... I had that, and here's what is was (fat chance).

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