ASR problem
 

I am nearing the end of my wits with this problem on my 93 600SEC. Here is what I have done to try to correct it over the past 8 months (basically have not been able to drive it normally):
1. went to several reputable Mercedes mechanics, paid each time to have the codes read. None could pinpoint the exact cause, but each suggested starting with a thorough wire harness check.
2. I completely replaced both MAF harnesses, all the way to the bottom connectors in the module box, checked continuity on all these wires numerous times. The originals were in a very sorry state, just a bundle of bare copper strands with plastic powder around them.
3. Removed both ETA's, opened them and checked all wiring from boards=to=plugs, all good. These harnesses were new, having both been replaced previously. Connected both harness plugs, with the ETA's sitting on top of the engine, and started the engine ( it will actually run this way, but since there is a complete lack of MAF feedback, plus no throttle, the engine rpm will slowly increase to a point where I have to switch it off). The purpose of this exercise was to allow a visual verification of the ETA function by depressing the accellerator pedal with the engine running, and both ETA's are acting normally.
3. Each time the engine is started, with the ETA' mounted back in place (after clearing all error codes using my Trisco scanner), the engine runs fine and revs up normally, for about 20 seconds, at which point the ASR light comes on, and Limp Mode is active.
4. The error code is the same each time, the LHI module check shows a code 17 ("MAF sensor voltage high or low or open wire"), for the LEFT bank only, the right bank reads "normal" every time).
5. I tried a process of elimination, by first swapping the 2 LHI modules - still the error is on the left bank, indicating that the modules are not at fault.
6. I thought it must be the MAF sensor, bought a new one, no change. Swapped the MAF sensors left to right, still have the 17 error on the left bank only.
7. Checked and re-checked MAF harness to module box continuity, all good.

The problem persists, and I have no idea what to check next. I would love to drive this car, but it has been many months (actually, it did spend 2 of these months in the shop to have the transmission rebuilt - the infamous slow reverse engagement probem which results in a mass of ground up springs in the pan....but that is another story - this car seems to be blessed with all the possible problems that have been reported as common to this generation, including the sound system,the window closers, and the A/C evaporator....) It is the ultimate example of a love/hate relationship at this point.

I'd be extremely grateful for any suggestions.

LH codes WON'T send the car into ASR limp mode. ONLY codes from the EA will affect the ASR system UNLESS the ABS lamp also comes on!

Scan the EA/CC/ISC system for codes, could be something as simple as overcharging.

IF you are getting MAS codes for the left side then check the MAS on the "right" side as well as the air intake rubber boots that attach to the intake on the RIGHT side.. The intake does cross, so the MAS on the right side is for the left side of the engine.