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  #1  
Old 10-11-2003, 11:08 PM
mike690003's Avatar
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300E fluctuating idle

Hello Board,

My 300E has a wierd idle problem, this happens in "P", "N", or "D". It idles at a steady 500rpm, and then will randomly jump to 700rpm . I have new vacuum lines and vacuum rubber and cleaned the idle control valve. I have new idle control valve hoses also. Does anyone know what could cause this wierd idle problem??
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1987 mercedes 300E
1995 e320 conversion(hated the 300e grill)
HID/Xenon (D2S)
Keyless Entry
Monochromatic Paint (Custom Blue)
Smoked Tails
Flat Badged (front)
Debadged (rear)
custom "carbon fiber" console
18 inch HP EVO rims
Sold! Now I drive a Monte Carlo SS
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  #2  
Old 10-11-2003, 11:17 PM
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Location: Southern California, U.S.A.
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There are other places where you can have a vacum leak.

We have a different engine with a different fuel injection system, but I had a fluctuating idle, and after replacing a lot of parts, the problem turned out to be a leak at the intake manifold gasket.

Two independent mechanics that specialize in Mercedes failed to find the leak, but the dealer found it in less than an hour.

The moral of the story is:

If you throw enough money at a problem, you are eventually going to fix it.
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2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".
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  #3  
Old 10-11-2003, 11:34 PM
JetForeman
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Do you have a vacuum gauge/pump that you can hook to it while it's idling? If not they're cheap and can be bought at most car parts places. I've used mine dozens of time from checking vacuum operated solenoids to sucking old brake fluid out of the resevoir before adding new. Very handy tool to have.
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  #4  
Old 10-11-2003, 11:53 PM
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Is the intake manifold gasket the one located on the airbox??
If so, I have replaced that circular rubber gasket.

I have replaced every visible vacuum line and rubber in the engine bay. Where else could a vacuum leak be coming from??
__________________
1987 mercedes 300E
1995 e320 conversion(hated the 300e grill)
HID/Xenon (D2S)
Keyless Entry
Monochromatic Paint (Custom Blue)
Smoked Tails
Flat Badged (front)
Debadged (rear)
custom "carbon fiber" console
18 inch HP EVO rims
Sold! Now I drive a Monte Carlo SS
http://memimage.cardomain.net/member.../352975_67.jpg
http://memimage.cardomain.net/member.../748335_24.jpg
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  #5  
Old 10-12-2003, 12:09 AM
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Mike,

I noticed your other posts regarding the coolant temp. sensor. If its not working correctly or unplugged it will make your car hesitate and run rough. Good Luck
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  #6  
Old 10-12-2003, 12:36 AM
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Is that the coolant sensor that controls the aux fan or is it the one that controls the CIS-EZL??
__________________
1987 mercedes 300E
1995 e320 conversion(hated the 300e grill)
HID/Xenon (D2S)
Keyless Entry
Monochromatic Paint (Custom Blue)
Smoked Tails
Flat Badged (front)
Debadged (rear)
custom "carbon fiber" console
18 inch HP EVO rims
Sold! Now I drive a Monte Carlo SS
http://memimage.cardomain.net/member.../352975_67.jpg
http://memimage.cardomain.net/member.../748335_24.jpg
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  #7  
Old 10-12-2003, 01:24 AM
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Join Date: Dec 2001
Location: Southern California, U.S.A.
Posts: 8,508
Quote:
Originally posted by mike690003
Is the intake manifold gasket the one located on the airbox??
If so, I have replaced that circular rubber gasket.

I have replaced every visible vacuum line and rubber in the engine bay. Where else could a vacuum leak be coming from??
No, the intake manifold is made of metal, sits on top of the head, and the gasket is not rubber.

In a combustion engine, a carburetor or fuel injection sits on top of the intake manifold, which directs fuel / air through the intake manifold and into the combustion chambers when the intake valve opens. When the pistons stroke to the top position, the spark plug fires, which ignites the fuel / air mixture, and drives the piston downward. When the piston is in the down position, the exhaust valve opens, directing the exhaust through the exhaust manifold and out through the muffler / tail pipe.
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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".
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  #8  
Old 10-19-2003, 06:38 PM
mike690003's Avatar
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Join Date: Apr 2003
Location: Miami,FL
Posts: 807
I have checked all vacuum lines today,they are all good and the car still fluctuates at idle. This happened right after I replaced the idle control valve hoses. Everything is hooked up.

Is my idle control valve going bad??

I have cleaned and wd-40'ed it to death.
__________________
1987 mercedes 300E
1995 e320 conversion(hated the 300e grill)
HID/Xenon (D2S)
Keyless Entry
Monochromatic Paint (Custom Blue)
Smoked Tails
Flat Badged (front)
Debadged (rear)
custom "carbon fiber" console
18 inch HP EVO rims
Sold! Now I drive a Monte Carlo SS
http://memimage.cardomain.net/member.../352975_67.jpg
http://memimage.cardomain.net/member.../748335_24.jpg
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  #9  
Old 10-20-2003, 12:53 AM
azhari
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Quote:
Is that the coolant sensor that controls the aux fan or is it the one that controls the CIS-EZL??
It's the one for the CIS-EZL.

Cheers.
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  #10  
Old 10-20-2003, 10:56 AM
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Join Date: Jul 2001
Location: SoCal
Posts: 1,303
"I have checked all vacuum lines today,they are all good and the car still fluctuates at idle. This happened right after I replaced the idle control valve hoses. Everything is hooked up."

In our 190E, when I did this I got the valve in backwards, with similar symptoms. Direction was counter-intuitive (intake below and outlet above), and even when I discovered the error, I don't know why it caused this behavior, but it did.

Steve
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