Hi, If any one can help with this most irritating problem it will be most appriciated. My 1983 380sec surges from 600-1000rpms once it heats up every couple of days.Some days it runs fine. I recently bought the car and it had some hesitation.My certified MB mechanic said the fuel frequency valve was disconnected. He cleaned fuel dist. set the lambda,new plugs. The car ran fine then the surge returned. He then adjusted fuel pressure. The The car ran fine then the surge came back after a few days. He then replaced O2 sensor readjusted lamda through hole in air cleaner. On the way home from the shop it surged for about 5 mins went away for a few days and returned again!

It's likely that your idle control module has a bad board or problems with it's harness at the module. I'd inspect the harness for corrosion and loose pin sockets first simply b/c the module is expensive to replace. If you're adventurous you can pull the idle module and remove it's board and resolder any questionable connections.

It seems you have honed right in on the problem. When I got the car I noticed the clip holding the idle control unit was in place but the nut was missing(it appears there was one nut on the drivers side and a clip on passenger).Which leads me to think it was fooled with. I did mention this to the mechanic but he seemed to think since the surging and associated bucking happened at all ranges of acceleration that it was not the problem. However, I will check the harness and if i can open the thing up & check the board as well. Thanks

The thing can be a bear to break open. Don't fret if you break a few clips as they encircle the entire opening. You'll see what I mean

I had the same thing happen. The connector to the idle control unit was falling off, since nothing holds it in place. It got knocked loose while cleaning leaves and debris inside the firewall.

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1985 380SE Blue/Blue - 230,000 miles
2012 Subaru Forester 5-speed
2005 Toyota Sienna
2004 Chrysler Sebring convertible
1999 Toyota Tacoma

First thing this am I checked out the idle control unit. It looked brand new inside and out the wiring harness looks fine as well. I have researched this forum but cannot seem to find a match for my problem. The closest post I found was from 11-11-2002 by M.B.Doc who stated these idle problems come from faulty sensor inputs to the CIS-e ignition control unit. I saw a aftermarket ignition control unit for under $60.00! Can any one recommend these units ?For that price I would be willing to gamble, although I don't want to be a "parts changer".Or is there a way to bypass the unit to see how it runs.We did this on my 1975 280S and it worked fine except the tach no longer functioned.

sec is still surging.It seems to run fine but if I turn the car off say to go into the store then start the car warm the surging returns. I did inspect the idle control module & wiring harness. I even unplugged it & it still surges. Can anyone please help ? The intermittent nature of the problem leads me to think its electrical. Thanks in advance.

I am having a similar problem to yours on a different model, different year. Let me know if you hear anything!

I am about to take my E420 1994 to a dealer for a diagnosis, unless someone gives me something solid in the forum to chase down.

Thanks,

LTurchin California

Not to discount the possibility of an idle valve or relay problem, but ...

Have you examined each and every vacuum hose and connecter closely for leaks, and to make sure that they are all connected? I chased this problem in my 560 and it turned out to be a small crack in the rubber connector for the cabin vacuum.

Also, are your idle air hoses in good shape?

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Well, I have just been informed that the surging has stopped. It seems the cis-e control unit was bad. The shop is also replacing the wires,cap,& rotor. If anyone needs a cis unit or also known as the "Lambda Brain" I got mine from Sun Valley Mercedes Dismantlers for the very fair price of $125.00 with a 6 month warranty. I will post a thread when I actually drive the car;as I have been dealing with the surge for almost 6 months. Thank You everyone for your input. Glenn

The car now runs like new. After months of chasing this problem changing the cis control unit, new wires, new cap & rotor has fixed the problem. Its great to have the car back again!