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  #1  
Old 11-11-2001, 05:07 PM
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W126 8 cyl. idle question

In the morning the car starts immediately and goes to a nice, fairly smooth 600 rpm idle. If I drive for 20 min. then turn it off, it will start and idle smoothly if I restart within 5 or so mins. after that and for the rest of the day, it will start and idle roughly for 20-30 seconds at about 500 rpms, it then goes up to 1000 rpms for a second and settles to a smooth 600 rpm idle. What are the probable culprits?
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  #2  
Old 11-11-2001, 07:01 PM
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Just a guess says that you are experiencing injector leakdown or fuel vapor lock (which would be caused by fuel pressure leakdown). Actually on second thought, probably just the vapor locking condition because if an injector or two were leaking down they would stay leaked down over night and you would have misfire till they pumped up all the time.

The reason this causes your idle symptoms would go like this: When cold, no vapor lock, car performs properly. When started after hot soak the car runs poorly due to poor fuel control with vapors in the injector and line (due to lack of residual fuel pressure - fuel boils at much higher temp when under pressure). Due to the fact that the engine is running poorly the idle control goes maximum open to try and maintain speed. The vapor locking usually clears after 15-20 secs and when it does the engine instantly runs right and at the higher rpm due to the valve being open. In a second or two the thing realizes its too fast and regains control and the event is over.
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Continental Imports
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  #3  
Old 11-11-2001, 10:23 PM
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Thank you for the reply Steve.

Where should I start to correct this problem? Should I be replacing injectors or is the fuel dist. at fault...or none of the above?

Thanks again
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  #4  
Old 11-11-2001, 10:42 PM
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Its a fuel pressure leak down problem, if I am right. That is easy to verify. Hook a fuel pressure gauge and watch what happens after shut down. If you can't do that then you need professional help.

I am not going to play spin the bottle.
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Steve Brotherton
Continental Imports
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33 years MB technician
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  #5  
Old 11-12-2001, 03:43 AM
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"I am not going to play spin the bottle."


I'm not sure how to reply to that......thanks?
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  #6  
Old 11-12-2001, 02:28 PM
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I replied to this earlier this morning and it got lost. Too bad cause I spent some time with it.

I didn't mean any harm by my comment, but I had just got off the road, returning from a half day seminar on late model MB diagnostics. I had to get up at 5 to drive 100 miles to Orlando and I was probably a little more sensitive to concept of random speculation.

The ending sentence was writen in haste after I wrote a paragraph starting to list the possible leaks. As I sat there contemplating it came over me and I erased it and declared the I wasn't going to speculate. If I could have expressed my mood better I would have tried to sermonize on my favorite gripe about this channel.

That being once I have spent some length in posts describing diagnostic technique, to see the thread continue on in random speculation: my car is blue so it most have been the wizbang senario.

Please excuse me I'll get over it.
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33 years MB technician
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