My 1990 240 DL kicked a 1-2-1 air mass meter code, along with the one to the oxygen sensor. The engine ran rough at start up but smoothed out when it warmed up. Following advice from the brickboard I cleaned the contacts on the AMM and the rough start up disappeared and car ran and does run smoothly now. Found another AMM on the brickboard, installed it to make sure it worked, and car still starts and runs smoothly. No more oxygen sensor code. The problem is that I can not erase the AMM 1-2-1 code. I followed the instructions in my Bentley manual, but they won't disappear and give me my 1-1-1 okay code. I had problems trying to erase them before when I changed out the throttle valve assembly when it kicked a 2-3-2 code because of oil in the throttle valve micro switch that made it stall at idle. Both these codes are still in the computer, though I feel there is now nothing wrong with either the throttle valve switch or the AMM. Do I need to replace the code reader, or is there still something wrong with the car that it won't let me erase any codes? The check engine light is still on after cleaning leads and replacing the AMM, so I am at a loss what to do next. Any suggestions greatly appreciated. Dick