Mercedes-Benz Forum banner

1 - 18 of 18 Posts

·
Registered
'13 911 Turbo S, '11 C63 AMG, 944 Turbo Track Car, '68 250SE CONV(2) 72 Unimog 411D, 85 190E 2.3-16
Joined
·
407 Posts
Discussion Starter #1 (Edited)
Well, I'm trying both the w129 and w124 forums looking for any member with this issue. I'm trying to sort out a w129 SL which has about 85K. It is my late father's car and it has an unusual problem.

The car had been sitting for some time and I found it with a dead battery; not surprisingly. After an overnight charge it started without issue, but after several minutes of running it developed an erratic/rough idle while in park. To my surprise it began to surge quite profoundly upon engaging drive and the car literaly lurched forward as the engine's revs went up and down, up and down. When placed back in park the idle returned to normal per se without any surging, but there is a slight "hunting" surge around 700rpm. Otherwise, the car comes alive when revved and has good power. In addition, the car is running very, very rich. An overload protection relay problem came to mind, but quickly realized the w129 chassis doesn't have one.

Upon investigation it was noticed that the fuses in the base module were intact but it was revealed that the engine wiring harness was deteriorating. I decided to replace it and start from scratch.

I am surprised to find that the problem still exists despite the poor condition of the harness.

In addition, just before the harness was changed I scanned the computer and got several codes, namely a "running too rich or too lean" code. Other codes included a "brake switch" and a "not communicating" code. There is no telling how long the codes have been stored or which ones are even relevant to the car's current status, therefore I will repeat the scan shortly and erase everything to start over and run the vehicle again.

The BW search option yielded several posts, but didn't seem to address significant surging while in gear.

Are there any members with similar experiences? My thoughts are beginning to focus around the resonance flap/idle control valve or electronic accelerator. Any ideas would be greatly appreciated. Thanks!

PS: After re-scanning the vehicle there are 2 codes:

1. "12 fuse F1 or control module n16/1"
2. "lambda 35 system operating at rich limit mixture too lean"

Anyone have information on the first?
 

·
W124 Moderator
86 190E 2.3L 16V, 2 95 320TE's, 02 S500
Joined
·
12,746 Posts
There are a couple of things to additionally check. Most often, idle surge problems are a result of a failed OVP regulator. Check that. Secondly, the wiring insulation material that deteriorates with the harness is also the same material used in the Electronic Throttle Actuator. That should be checked. Best to build a code reader and see what's up. What year is the SL?

Jayare
 

·
Registered
'13 911 Turbo S, '11 C63 AMG, 944 Turbo Track Car, '68 250SE CONV(2) 72 Unimog 411D, 85 190E 2.3-16
Joined
·
407 Posts
Discussion Starter #4
There are a couple of things to additionally check. Most often, idle surge problems are a result of a failed OVP regulator. Check that. Secondly, the wiring insulation material that deteriorates with the harness is also the same material used in the Electronic Throttle Actuator. That should be checked. Best to build a code reader and see what's up. What year is the SL?

Jayare
Exactly like a bad overload protection relay but this car doesn't have one. The bas module functions as an OVP relay would in a W124 chassis.

But over the weekend I was lucky enough to find and replace the electronic throttle actuator with a rebuild unit that a friend had in stock and........NOTHING!!!!!!!!!!!!! The same exact problem after installation:eek:

I have even checked the rubber intake boot between the ETA and plastic cross tube to the Mas sensor for breaks as I remember seeing a car with a hairline crack in one developing a vacuum leak with all sorts of weird problems.

Both fuel pumps are running but didn't do any fuel pressure check as of yet. The vehicle also has all new ignition coils.

Upon start up the car runs very well; could even pass for perfect but for a slight shake. Then as it leaves cold start cycle after the air pump shuts off it begins to miss slightly until and after about 10 minutes goes into a full-fledged hunt/surge shaking. When placed it gear it gets wicked; the car starts lurching like it were in a rocking chair.

Still getting a Lambda 35 mixture rich/lean code. Oh well back to the drawing board:surrender:
 

·
Registered
'13 911 Turbo S, '11 C63 AMG, 944 Turbo Track Car, '68 250SE CONV(2) 72 Unimog 411D, 85 190E 2.3-16
Joined
·
407 Posts
Discussion Starter #5
Additionally,

The large side cover of the ETA was removed to physically inspect the wiring and printed circuit; the wiring insulation was starting to come off.

This can confirm a bad unit, even without codes being present. Not in my case, however.
 

·
Registered
'13 911 Turbo S, '11 C63 AMG, 944 Turbo Track Car, '68 250SE CONV(2) 72 Unimog 411D, 85 190E 2.3-16
Joined
·
407 Posts
Discussion Starter #8
The base module is the OVP on this car. 2 15 amp fuses in the top. It's about the size of an ECU. Never heard of anyone having to replace one though bad harnesses and shorts in ETA's have ruined other components I've read.

The fuses for the BM are getting power.
 

·
Registered
'13 911 Turbo S, '11 C63 AMG, 944 Turbo Track Car, '68 250SE CONV(2) 72 Unimog 411D, 85 190E 2.3-16
Joined
·
407 Posts
Discussion Starter #9
only the 300 and 500 129s had an OVP, the base module performs the functions.



how long is 'some time', time can do some funky things to the fuel system on these cars :(




Fish
Probably sitting in storage for most of the last 12 months with a full tank of fuel. Driven maybe a total of 50 miles during that time.
 

·
Registered
'89 300TE, '79 450SL, '01 ML320
Joined
·
1,051 Posts
Okay, that's not so bad, prolly a non issue. Harness and ETA would be my first guess, but you've
taken care of both. Sorry, I can't tell you anything you don't know already :(

Edit: Any chance you can put your hands on a spare MAS? Also, could a bad O2 sensor be tripping the lambda code?

Fish
 

·
Registered
'13 911 Turbo S, '11 C63 AMG, 944 Turbo Track Car, '68 250SE CONV(2) 72 Unimog 411D, 85 190E 2.3-16
Joined
·
407 Posts
Discussion Starter #11
Yeah thanks. I'm in uncharted territory as well here. Anyone ever changed a Base Module?
 

·
Registered
'13 911 Turbo S, '11 C63 AMG, 944 Turbo Track Car, '68 250SE CONV(2) 72 Unimog 411D, 85 190E 2.3-16
Joined
·
407 Posts
Discussion Starter #12
Okay, that's not so bad, prolly a non issue. Harness and ETA would be my first guess, but you've
taken care of both. Sorry, I can't tell you anything you don't know already :(

Edit: Any chance you can put your hands on a spare MAS? Also, could a bad O2 sensor be tripping the lambda code?

Fish
Amazingly my friend gave me 3 used units to plug in and no change. Interesting comment about the Lambda code. Doing all the work at my late fathers house; he has a workshop with lift in his detached garage. Came across last night a rear four wire O2 sensor possibly either belonging to the car or ready to go in as it looked fairly new, but the car has two and din't check the forward one near the right side trasnmission tunnel.

Remember years back of a car that ran like dirt. Replacing ONE sensor cured some serious driveability issues on a customers vehicle. The 103 and 104 engines are great runners but can develope some strange hard to trace issues particularly due to the whole wiring [email protected]%#ck up of the early 90's.
 

·
Registered
'89 300TE, '79 450SL, '01 ML320
Joined
·
1,051 Posts
I think the second one is only to sense after the cats for emissions, no control over the computer.
Pretty sure the first one has control over the mixture. Ive never changed a base module,
or heard of anyone changing one. But I've only worked on a handful of equipped models.
I'm just getting back into the game after taking several years off to smash my thumb with a hammer
instead of scraping my knuckles off :)




Fish
 

·
Registered
'13 911 Turbo S, '11 C63 AMG, 944 Turbo Track Car, '68 250SE CONV(2) 72 Unimog 411D, 85 190E 2.3-16
Joined
·
407 Posts
Discussion Starter #15 (Edited)
1994

Going to change the forward O2 sensor tomorrow. Pulled some live data with the old Assenmacher (not the newest technology) and the mixture seems to be running wild from low to high which might explain the Lambda "mixture too rich or too lean" fault.

Could have sworn it said O2 sensor #1 was "off".
 

·
Registered
'13 911 Turbo S, '11 C63 AMG, 944 Turbo Track Car, '68 250SE CONV(2) 72 Unimog 411D, 85 190E 2.3-16
Joined
·
407 Posts
Discussion Starter #17
:thumbsup:

Update:
After much grief and bewilderment there is some good news. Turns out that after using a quality scanner/computer I was able to do a thorough reset of adaptations on the vehicle. The Assenmacher tester I had from the 90's had the reset adaptations option, but was not able to do the job for some reason; I used a LAUNCH scanner that a friend just purchased instead and voila! No surging, hunting or rough idle any longer.

The job cost about $900 between the new harness, rebuilt ETA and front O2 sensor. It's hard to say what I didn't have to replace. The engine wiring harness was beginning to fray, but may have still been OK. The ETA was also inspected and found to have deteriorating wiring inside.

Thanks for all suggestions and hopefully this thread may be of use to someone one day.
 

·
Registered
1997 SL320 Glasstop
Joined
·
51 Posts
:thumbsup:

Update:
After much grief and bewilderment there is some good news. Turns out that after using a quality scanner/computer I was able to do a thorough reset of adaptations on the vehicle. The Assenmacher tester I had from the 90's had the reset adaptations option, but was not able to do the job for some reason; I used a LAUNCH scanner that a friend just purchased instead and voila! No surging, hunting or rough idle any longer.

The job cost about $900 between the new harness, rebuilt ETA and front O2 sensor. It's hard to say what I didn't have to replace. The engine wiring harness was beginning to fray, but may have still been OK. The ETA was also inspected and found to have deteriorating wiring inside.

Thanks for all suggestions and hopefully this thread may be of use to someone one day.
May I ask what exactly does "reset of adaptations" do to the vehicle? Is it reset the computer to, say, some initial state?

Many thanks.
 
1 - 18 of 18 Posts
Top