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Mercedes-Benz 560SEL mod 91,MB 560SEL mod 90
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Discussion Starter #1
Hi everybody,

Nowadays, I when I start my car, I can hear my Idle increases and decreases "slight change" for a few minutes. When engine got hot enough, it disappears. I noticed this just after I changed the FD and the fuel regulator. The idle is smooth except this very little surging. Do the FD and regulator are set together? any help would be highly appreciated and thanks.
 

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1993 300TE, 1995 E320 Wagon
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1,895 Posts
Sounds to me like it's your idle speed control relay that's causing this. It doesn't sound too major at this point, but you might see if you can swap in a "known good" one from another source. The relay is behind a false wall in the passenger-side footwell. Remove the carpet and you will see a black plastic "wall" with a 10mm nut in a recess at the bottom. Remove this, and the relay is up on the wall about 6 inches from the floor, in a little holder. Probably #006 545 8532 or 004 545 1132.
 

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1995 E320 (totalled) 91 420SEL W126 (retired) 2002 S500 W220(retired); 2008 C300 Sport W204
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662 Posts
It may be a vacuum leak at the fuel pressure regulator vacuum line. Re check for leaks.
Even after warm up, does the car have this surging issue at driving speeds of 55 to 65 MPH?

My car had similar symptoms on startup and I fixed it:
With car running and air box removed:
One at a time, crack each fuel line at the FD until fuel seeps out.
Tap the top of the FD with a small hammer.
If this is the issue, you should see some black or dirty fuel come out of the cracked fuel line.
After the flow runs clean retighten and go to the next fuel line.
After this process, the surging feeling was gone.
 

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Mercedes-Benz 560SEL mod 91,MB 560SEL mod 90
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500 Posts
Discussion Starter #4
It may be a vacuum leak at the fuel pressure regulator vacuum line. Re check for leaks.
Even after warm up, does the car have this surging issue at driving speeds of 55 to 65 MPH?

My car had similar symptoms on startup and I fixed it:
With car running and air box removed:
One at a time, crack each fuel line at the FD until fuel seeps out.
Tap the top of the FD with a small hammer.
If this is the issue, you should see some black or dirty fuel come out of the cracked fuel line.
After the flow runs clean retighten and go to the next fuel line.
After this process, the surging feeling was gone.
The car does not have this surging issue at driving, only while engine at warming up, then it disappear. I noticed also while driving at low or high speed, there is like cut off fuel :confused: for a fraction of second as soon as I take off my foot from the fuel pedal. I will check for vacuum air leaks and do fuel purging through out the FD at each fuel line and see.
 

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Mercedes-Benz 560SEL mod 91,MB 560SEL mod 90
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500 Posts
Discussion Starter #5
I removed the air filter housing , checked for air vacuum leak and found nothing.
I gently touched the center plate and found it touching at one side and not moving smoothly. Loosed its mounting bolt and placed it correctly, cranked engine and observed idle and found no more surging. The realy matter now is why there is like fuel cut off as soon as I removed my foot from the fuel pedal and car keeps just rolling as if there is no fuel unless I put my foot again.
Please guys I need your help here and thanks for your cooperation.
 

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Did you change the FD with the attached EHA

If not I thought First you need to adjust the idle air with 3cm hex

if cut off not going readjust EHA with expert and adjust air0fuel Mixture
 

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Mercedes-Benz 560SEL mod 91,MB 560SEL mod 90
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Discussion Starter #7 (Edited)
Did you change the FD with the attached EHA

If not I thought First you need to adjust the idle air with 3cm hex

if cut off not going readjust EHA with expert and adjust air0fuel Mixture
I have changed both FD and EHA but the latter has been removed from different FD which I was not sure if it is good or bad. I can do the air/fuel mixture adjustment very easily because I did replace and adjust many of the FDs before, I have no doubt about it.
I can do also the adjustment of the EHA by unscrew the flat screw at the back and adjust the elan key which is inside, I turn it fully CW then I turn it back CCW for 5 to 7 turns and will work accordingly to the adjustment of the plunger inside the FD. If the plunger is inserted little bit more inside " more rich", the more turns of the EHA screw will be set to CCW" lean" and vice versa. I think my problem is the EHA that I do not have a good one, all what I have tested are used ones.
 

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Greek God of the R129
SL500-500SEL-190E
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8,391 Posts
The fuel pumps get a signal from the oil pressure sender unit, and throttle .
In an accident the fuel pump should cut off.

CK the connector on the oil pressure sender.
(By the oil filter housing.)

Oil and dirt will mess the signal.

By pushing on the throttle this signal overrides the other/oil pressure....

Regards,
aam.
 

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Discussion Starter #9
The fuel pumps get a signal from the oil pressure sender unit, and throttle .
In an accident the fuel pump should cut off.

CK the connector on the oil pressure sender.
(By the oil filter housing.)

Oil and dirt will mess the signal.

By pushing on the throttle this signal overrides the other/oil pressure....

Regards,
aam.
Today, I will check the oil pressure sender connector. If it is okay, is there
a possibility to be the throttle switch is miss-adjusted or bad?
 
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