I'm sure this has been addressed before, but for the life of me I can't find it anywhere on the forum after several hours of reading. I have a 1988 300 SEL that just began having surge/decel problems yesterday. While traveling at freeway speeds, it feels as if I lose power or decelerate for a half second. It feels similar to what you experience when you pass a semi at high speed on the freeway and as you pass you are buffeted by the wind to the point where you are momentarily thrown off course. My RPM's don't seem to change when this happens. The sudden decel seems to happen every couple of minutes as I travel. Then when I am at low speed (in a parking lot or coasting to a stop) I feel surges of extra speed. While at stoplights the idle RPM is higher than normal with a basline of about 800 instead of its usual 650 and the RPM fluctuates between 800 and 1500. There are no idiot lights on.
The morning this happened, I was changing out the brushings in the blower motor. Now this is a 126, so I accessed the blower from the passenger kick panel, not the engine compartment. Can't think of anything down there that I could knock off to cause this though.

So anyone have any thoughts as to where to start? Does the OVP cause such intermittent problems? My understanding was that if it went bad it would be in a limp home mode and my ABS light would be on. Can a bad fuel pump relay cause these sorts of symptoms? Let me know what you think. THANKS!

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Eric Zacharias

'88 300 SEL
'64 Ford Falcon
'99 Infiniti QX4

My sugestion... because it is so easy to check... is to unplug your 02 sensor (under passenger carpet) and see if thats causing it.

I had some of the same symptoms... which were solved by replacing the O2 sensor.

good luck... hope it's just that simple.

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-Marty

1986 300E 220,000 miles+ transmission impossible
(Now waiting under a bridge in order to become one)

Reading your M103 duty cycle:
http://www.peachparts.com/shopforum/showpost.php?p=831799&postcount=13
http://www.peachparts.com/shopforum/showpost.php?p=831807&postcount=14

Here's another clue. Today the SRS light came on briefly while freeway driving, for about 3 seconds, and then went off. Could be related, could be a red herring.

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Eric Zacharias

'88 300 SEL
'64 Ford Falcon
'99 Infiniti QX4

Possible OVP relay problem.
Do as suggested first though...unplug the O2 under the passengers side front carpet and test drive.

This condition is also presents when the CIS-e is not set to correct frequency.
At idle the idle stabiliser tries to fight the lean/rich swings causing the idle speed to hunt.

Another thing...this happened on another, a 300e...the lower fuel pump was begining to fail.


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[http://languageandgrammar.com/2008/01/14/youve-got-problems-not-issues/ ]

"A liberal is someone who feels they owe a great debt to their fellow man, which debt he proposes to pay off with your money."

Check your alternator voltage regulator and brushes. I had a similar problem once in my 300se. Happened as you describe several times then finally died on the side of the highway. The brushes were barely making contact and I was running very low voltage. The fuel pump and SRS lights seem to be the first to give signs of low voltage.