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Old 12-11-2010, 02:48 AM
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Join Date: May 2007
Location: New Jersey
Posts: 95
sorry, another e320 rough idle thread

sorry all for another 94 e320 idle thread, but I am at my wits end. Tonight on my way home in traffic, I did not know if I was going to rear end someone or the car was going to stall first. Idle would surge and had to keep brake on good to not hit car in front of me. A few moments later, idle so low that would almost stall (this continued for about 10 minutes). traffic cleared, sped up to 65 and car drove the rest of the trip like new. Even stopped at a couple lights and no idle issue.

some background: not sure if harness is newer one. I do know there is a white tag on the harness by the battery, but the date codes have rubbed off. A few months ago car developed a rough idle after i had a misfire issue that was corrected by replacing a bad coil. I figured the O2 sensor got messed up from the misfiring so I replaced that and seemed to help very little, but continued to drive months with the rough idle.

A few weeks ago at stop lights idle would surge up and down then got CE light a few days later. pulled the following codes

built in
code 10 - Voltage at mass air sensor too high/low
pin 8
code 4 - Hot film mass air flow sensor
code 13 - 13 O2S (Lambda) control system operating at rich or lean limit
pin 14
code 11 - Closed throttle recognition signal to engine control module (HFM-SFI or Left LH-SFI)
Fuel safety shut-off to engine control module (HFM-SFI or left or right LH-SFI)

cleared codes and replaced MAF sensor with a brand new aftermarket unit. I know from experience that w124's hate non-oem parts, but the price was too good to pass up.

past few days car would drive fine no idle issues until would drive to a store, shut off car for a few minutes, and then when start again would struggle not to have an idle surge while leaving the parking lot (car did this two separate days)

all the above is when its 30 out and car is warming up or completely warmed up

tonight when got home and checked codes only code 13 on pin 8 was present. My next thing to check under the hood is the vacuum lines under the very front black cover of the engine and the fuel pressure regulator ... sorry for the long post, but any suggestions?

Thanks in advance

1994 E320, 145,000 miles
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Old 07-23-2013, 11:34 AM
Registered User
Join Date: Sep 2004
Posts: 1
Lafooy, I have a 95 e320 with the same symptoms and codes. Curious as to whether you were able to sort out the root problem and find a solution......maybe an OEM maf sensor or?
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Old 07-23-2013, 12:09 PM
Registered User
Join Date: Jun 2012
Posts: 228
My vote for OEM MAF as well or the wiring that connects to it. See if you can get a refund for the aftermarket and get one from peachparts or ********AZ

I'm dealing with misfires and hesitation on my 1995 E320 with ASR, but i'm waiting for BBA to take care of my Throttle Body, since that's an obvious cause.

If you want to see if your harness is good or bad, cut the outer isolation from the cable that goes to the MAF sensor. That's the hottest spot of the harmness since it sits right on top of the exhaust manifold.
The wiring to the MAF is the first to go bad.
If you see degraded isolation, than that's your issue. You can either replace just the leads to the MAF, if you're on a tight budget and pray that nothing else will short, or replace the complete harness. (Used ones with a newer build date can be found on CL or ebay) But brand new is the best option if you can afford it.
If your isolation is degraded, than your throttle body is most probably on it's way out.

The wiring isolation on this cars was made with the idea that it will disappear in 15 years. Shorted MAF, ETA ori O2 sensor can damage your ECU and that's something to keep in mind as well.
I had a bad coil that shorted the ECU, but luckily i was able to just restore the pin on the board of the ECU and it worked fine

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