Misdiagnosed '94 SL320

[johneurostar]

Hello everyone. I'm in the process of sorting out a w129 SL with the M104 engine and 85K. It was my late father's car who passed away recently.

The car had been sitting for some time and I found it in his garage 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 even began lurching forward as the engine's revs went up and down, up and down. When placed back in park the car resumed it's rough idle. Additionally, the car is running very, very rich. Extremely rich. An overload protection relay came to mind until it was quickly realized there was none.

The fuses in the base module were found intact, but it was revealed during close inspection that the engine wiring harness was deteriorating so it's been replaced. In the past that always cured weird problems, but this time my luck finally ran out; the problem still exists

So the memory bank began churning back to the days when my father and I worked together ago in our family-owned MB repair shop. However the years gone by have required me to engage in some serious memory recollection.

Eventually previous cases came to mind. There were many weird problems that were encountered with M104 electronics; namely W124 chassis cars. Most of the challenging cases, usually with non-descript scanner codes, were directly attributable to faulty harnesses or even electronic accelerators.

The codes I was able to retrieve were acquired using an Assenmacher tester with the 38pin "mushroom" plug. The codes are "12 fuse F1 or control module" as well as "Lambda 35 system operating at rich limit mixture too lean" error codes.

Last night my friend gave me several air flow sensors to plug in as testers without effect. In the old days I always kept several electronic accelerators which were used as test units to diagnose problem cars, but that luxury is gone.

My gut tells me to change the O2 sensors but before more parts get thrown into the vehicle, perhaps something has been overlooked?

Any ideas would be greatly appreciated!