Hello. I'm new to the forums and such, but certainly not Mercedes-Benz. I'm much more familiar with the Diesels, going back to the W115. My newer gasoline Mercedes is becoming quite the headache!
I have a 1997 E320, with the M104 straight-six, and automatic transmission. The ASR light is on immediately when the car is started, and stays on. This is the only light illuminated, so nothing with the ABS or such. The car has absolutely NO throttle response. Once it's warmed up, tapping the gas pedal merely causes the idle to kind of "flutter" or "drone" up-down-up-down from then on. The car will idle around in Drive or Reverse, but at perhaps 3 MPH. There are no OBD-II codes.
I've been reading up on this for quite a while now. How do I determine what's wrong? There is no cable going to the throttle body. I swapped the brake switch with 3 known good ones. There is no place to attach the flashing LED scanner, like in the older models. How do I proceed?

Please make sure this is a 97 Model year as the 96 system is way different. What is the build date?

Does the throttle cable only go to a sensor on the left fender or does it go to the engine?

With either model year, you will need a scanner that plugs into the under hood 38 pin connector. Only the engine will come through the under dash OBD connector. Also be aware that there are 38 pin to OBD 2 adapter cables but this will still only get you the engine side.

-The car was built on 3/97. The throttle cable does indeed go to the sensor near the firewall and fender.
-I have an adapter that allows my OBD-II scanner to plug into the 38-pin connector. I've used this in the past to work on other cars. However, it only allows me to get "generic" P0XXX codes. I can't get anything from the SRS, ABS, or transmission, for instance.

You need to get to the ABS / ASR computer data / codes to figure this out. I'd probably unplug the ABS / ASR computer and see what happens. I haven't done this and am assuming this won't cause some sort of engine side fault code / limp.

Somewhere on this list there is a procedure to jumper something in the 38 pin to fully disable ASR for dyno testing.

This car should have an ASR off button in the radio area switch bank, have you tried this? According to others, this only reduces but not totally eliminates ASR.

The ABS / ASR is bolted to the engine computer , it is about 1" thick x 10 " long and 4 " high. It will be marked ASR and / or ABS

The 97 ME 2.0 / ME 2.1 is full drive by wire, the ASR first reduces throttle and it this does not work, it applies rear brakes on rear wheels that exceed some % of front wheel speed.

The W210 seems to have grounding corrosion issues, have a look at the under hood ground points and take them apart for cleaning. Someone else had a no run condition that was traced to a bad ground near the passenger side computer box. I have a 97 W210 parts car that intermittently has trans limp mode / left fog light on and high beam indicator on the dash that I'm betting is a ground issue.

-Thanks for all the recommendations. I'll have to open up the box with all the computers, and see which one is dedicated to the ASR. Going through grounds is always sound advice, as well! There is the ASR OFF button by the shifter and window switches; I don't remember this making any difference. It looks like I have a lot more ideas for this weekend.
-I'll try to see if something can be jumped in the 38-Pin connector, although I really want to have my facts straight before I jam 12 volts into anything!

-More investigation into the problem, but no real progress. Hitting the "ASR Off" button changes nothing. I checked as many grounds as I could find, and even add new ground straps between the engine and the body.
-There are a whole stack of modules in the box on the passenger side. I replaced the big "relay" with all the fuses; no change. The transmission controller was replaced last summer when I fixed the transmission. There are 3 other modules. I have ones from another 1997 E320, but I think the ASR cars use different computers. The build dates on the computers are within one month, but the connectors and descriptions are different.
-The Throttle Body itself may be the problem. With the engine running, there is no movement I can see. Also, it is part number 112 141 00 25. I thought 112 would be for the newer V6 engine, but there it is on my M104...

Follow up with my E320. I finally got it back from the dealership. I guess the problem all along was over- and under-voltage spikes. These occurred too often, so the computers finally put the car into limp-mode. They said the ASR system is the most sensitive to this, so it's the first to react.
A simple clearing of the computers with a dealer scan tool, and I guess I'm back on the road. It looks like this is something I couldn't have fixed myself...