The post with the code reader construction and use is here:
http://www.benzworld.org/forums/w124...tic-codes.html
Code reader connections are black lead (ground)to pin 1 of the 16 pin connector
Red lead +12 to pin 16 or the + battery terminal nearby
Probe or yellow lead to the pin you are pulling codes from
IGNITION SHOULD BE IN THE ON POSITION
Press switch for 2 seconds, release and count the pulses of the LED
Do it again for next code...
Do it again for next code...
Do the above until you cycle back to the first code read.
One blink means that it's working and there are no errors
To reset each code number...
After the code is read, to clear that code, press the button for 5 - 6 seconds only (not longer or shorter). If you see it pulsing a code again, you held it too long or too short. After you clear all the codes on a particular pin, try reading them again. If they are still there, try to reset again. I had trouble and was not able to reset all codes all the time.
Bottom-line... when I replaced the MAS, the code 4 did not show up anymore and neither did code 13 (O2 lambda out of range). I was correct that the MAF being messed up affected the operation and reading at the oxygen sensor which was not bad.