'94 E320T S124 M104 - Won't Idle, Unknown Code
 

Hi, All.

I'm having problems with my '94 E320 tourenwagen; here's the lowdown:

The car was running perfectly, but had a starter problem that turned out to be the neutral safety switch. I don't have facilities to get under the car for that kind of work (plus I'm getting too old for it), so I had a local indie take care of it. Once again, the car was running perfectly.

Several days later, I go out to take a ride, start the car, she starts and runs for a second or two and then goes completely dead, with no lights on the dashboard. I try to restart, and get absolutely nothing: no clicks, no lights, nothing. So I lift the hood and see that the the indie was careless and hadn't properly tightened the negative lead at the battery terminal, as it's laying there loose. I put everything back to normal, the car starts right up and runs strong like she always has, pulling like a freight train all the way to redline and shifting clean, but won't idle.

Idle speed is around 400-500 RPM when she does idle, but surges, stumbles and stalls whenever I come completely off throttle. I swapped the OVP from my other '94 E320T parts car and it made no difference. Using my trusty Dalton code reader, I cleared the codes and drove around a bit, and the only two that came back are 47 and 49 on pin 8. Engine wiring harness has been replaced, no blown fuses in the underhood fuse box, 234k miles.

Code 49 is "Voltage supply at engine control module implausible/low volts" but none of the listings I'm able to find show a code 47 for pin 8, so I'm hoping y'all can give me some guidance on that as well as anything else to check.

Best Regards,
Rob

What is the system voltage when the engine is running? I've seen overvoltage mess with idle control.

14.9 Volts.

How High is Too High?
 

Is 14.9 Volts too high?

It is a bit on the high side but IIRC it has to be over 16V before it will screw with the idle.

Started my 93 with a loose battery ground and it immediately destroyed an engine ground connection underneath near the bell housing. It was a black approximately 12 or 10 gauge wire held in by a 10mm hex head bolt. It is worth a look.

Otherwise try swapping the MAF sensor from your other car. Also try rapping on the current MAF sensor with the car running to see if you can get the idle to change.

Good luck!!!

Thanks for the suggestions, all. I'll be away for the next two weeks and will have a go at it when I get back.

14.1 to 14.5 is the normal range for alternator max charging voltage. 14.9 might be your meter calibration (digital?) or it could be a poor regulator and at that voltage may boil away your battery juice faster than normal. I suggest looking into that later, after you find the gremlin in the idle control.
#1 - Check all fuses.
#2 Ques: Did you drive at night and if so were the headlights brighter than normal at any time?
An unloaded alternator may exceed the normal system voltage and I hate to say it but its possible a module failed because the battery terminal came loose.
Be sure and let the Indy know. He may need to repair or replace something at his expense .. ?
I had a friend with a CB radio in a Chrysler product where the battery came disconnected and it fried the CB radio and a few other things.
DDH

I bought a brand new OVP relay and swapped it in, just in case the one from the parts car was bad, also swapped in the MAF from the parts car, no change from either. Pin 8 is still showing codes 47 (not listed anywhere/unknown code) and 49 (Voltage at engine control module implausible/low Volts) and now also showing code 13 (O2/lambda control system operating at rich or lean limit). All the fuses are okay and the lights are as bright as they've always been when driving at night.

Any help here?

The only codes 47/48 I see are related to injector 6.
http://www.w124performance.com/docs/mb/diagnostics/DTC_List_W124_M104.pdf

Thanks, Hirnbeiss; I already have that document.

The 047 code that you're seeing listed second in the first column there is what's shown by the HHT (Hand-Held Tester) digital code reader, corresponding to the 19 code listed first in the first column, which comes from the pulse counter. The 47 code to which I'm referring is from the pulse counter, which you can see is missing from the first list in the first column.

However, the third column, "Test Step/Remedy" for the 49 code I'm getting from the pulse counter references what appears to be a procedure of some type in some other document. Does anyone know what this document is and where I can find it?