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'82 Euro 500SEL, '85 Euro 500SEC AMG WB Cabriolet,'86 Euro 500SEC RUF
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Discussion Starter · #1 · (Edited)
Surging Idle Fixed.
Even after I had the local Indy set the CO mixture and check the timing the idle is still at 500 RPM warm or cold. I had an idle surge of a hundred RPM or so and finally cured it.
When I replaced all the rubber hoses in the car the two Elbows on the Idle Control Valve had the bypass tube between them, like the later models. One end of the tube was crimped and sealed shut. Thinking it should be open to work right, I opened it up. I had also changed out the ICV with a Gen II one.

Searching for the surge, I changed the ICV back to my working Gen I ICV. and I plugged the end of the bypass tube.

Voila! The surge was gone, cold or warm. Not sure and I don't really care which one of the two changes or both worked, but I'm guessing the the bypass tube being open(in a Gen I Euro) is a no, no, as the original rubber Elbows had no holes or provisions for the bypass tube. Later part numbers had the ports, but not drilled, and the latest part numbers have both the port and the holes cast in.

Gen II EZL in a Gen I Car.
Another thing I discovered, in a pinch, a Gen II EZL will work in a Gen I car. One simply plugs the 4 pin plug into the corresponding 4 pin on the EZL bottom right looking at the EZL, then plug the TDC Sensor wire into Crank Sensor plug on the top of the Gen II EZL. Good to go!
 

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83 500SEC, 87 300D, 92 190E 2.6, 02 C32, 02 C32T, 03 C320T4, 03 E55, 05 CDI, 06 CDI
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2,601 Posts
Nice. I should have a spare euro gen 1 EZL soon, there was a box from MSD sitting on the porch when I came home tonight :D
 

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2019 Hyundai Elantra, 2005 Chrysler Town & Country, 1999 GMC Yukon
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1,660 Posts
Mine recently went from a low idle (~550rpm) to an occasional 1100rpm. I DON'T like the way it bangs into D or R from P at that speed, so I'll be looking to do the same to my car next week, I hope.

I need to replace all the vacuum lines in my car anyway.
 

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'82 Euro 500SEL, '85 Euro 500SEC AMG WB Cabriolet,'86 Euro 500SEC RUF
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9,498 Posts
Discussion Starter · #4 ·
That's fun job. When you take the air plenum off to get at the lines under the manifold, replace the 3/2 valve on the throttle body and clean the throttle body. Replace the Throttle position sensor and a new gasket for the throttle body. And if they haven't been replaced lately, replace the doughnuts and the intake manifold gaskets. My manifold doughnuts and intake gaskets were replaced less than 30,000 miles ago so I didn't do it.
Probably should have, but it's just an hour or so to get down to the throttle body.
 
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