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  #1  
Old 06-02-2019, 07:58 AM
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Join Date: Jun 2002
Location: Northeast
Posts: 231
1980 450sl rough idle - no power

So, I couldn't leave well enough alone. I had to have cruise control...

As I was messing with the cruise control - reinstall it and troubleshoot it, I decided to mess with the fuse marked cruise control - #10.
Of course not wanting to do things correctly and turn the car off, disconnect the battery, I did it with the car running.
So I clean #10 and I think let me clean some of the other fuses, specifically #8 which deals with emissions. I notice when I removed the "emissions fuse" the car would idle differently - the idle went up when removed. I clean it put it back and as I clean things up and start the car back up it now has a rough idle and no power.

It was so bad, the car had trouble backing up a slight incline of my driveway.

It was getting late, I didn't do much troubleshooting and left it for another day.

Based on what I did, does anyone have any idea where to start. The car ran perfect before me messing with the fuse box.

Alot of good the cruise control does me now.

Thanks.
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  #2  
Old 06-02-2019, 10:49 PM
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Join Date: Feb 2011
Location: Modesto CA
Posts: 2,748
Quote:
Originally Posted by junker68 View Post
So, I couldn't leave well enough alone. I had to have cruise control...

As I was messing with the cruise control - reinstall it and troubleshoot it, I decided to mess with the fuse marked cruise control - #10.
Of course not wanting to do things correctly and turn the car off, disconnect the battery, I did it with the car running.
So I clean #10 and I think let me clean some of the other fuses, specifically #8 which deals with emissions. I notice when I removed the "emissions fuse" the car would idle differently - the idle went up when removed. I clean it put it back and as I clean things up and start the car back up it now has a rough idle and no power.

It was so bad, the car had trouble backing up a slight incline of my driveway.

It was getting late, I didn't do much troubleshooting and left it for another day.

Based on what I did, does anyone have any idea where to start. The car ran perfect before me messing with the fuse box.

A lot of good the cruise control does me now.

Thanks.

Two scenarios of potential faults:
Red -
When the controller for the frequency valve was powered down, mixture control reverted to open loop, which is a bit richer than what would be the controlled mixture, hence a slightly higher idle speed.

Magenta -
Removing and restoring power to the controller while operating likely caused a voltage spike, a spike which may have damaged one or more solid state components in the controller, resulting in a mixture that is either way rich, or way lean; probably lean.
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  #3  
Old 06-03-2019, 10:14 AM
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Join Date: Jun 2002
Location: Northeast
Posts: 231
Thanks Frank,

I'm going to tackle this during the week. I'll keep the forum appraised. It's always nice to get the result of given problems related to the cars we enjoy.

Dwayne
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  #4  
Old 06-16-2019, 09:49 AM
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Join Date: Jun 2002
Location: Northeast
Posts: 231
Thanks again Frank!
Bought a used controller and my baby is back to her old self. Lesson learned... and I've got cruise control!
While I was at it, I installed a new O2 sensor along with a grounding strap, which has been addressed in a few threads.
The car runs better than ever - thanks again!
Dwayne
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