Having searched the archives and found a similar discussion, I was hoping to request further clarification. The originator of the original discussion is graciously assisting me in figuring out this problem, but I wanted the collective wisdom of all members. My check engine light came on, although the car seems to be running well. I pulled code #19, and have seen the TSB which calls for a replacement computer, particularly in the Jacksonville area. I live in Southern California, and this has apparently always been a California vehicle.

I obtained a replacement computer from a salvage yard bearing the same part number, despite knowing that a new part number was available, since this had taken care of the problem for another member. For nine days, the check engine light stayed off, but then suddenly reappeared. Clearing the code out and shorting out the 1 and 4 connectors did not prevent the check engine light from coming back on very quickly (less than 30 minutes of driving). I am sending the computer to this other member as he was friendly enough to try it out in his car to see if we could isolate the problem to either my car or the computer. Now that I have switched back to the original computer, the light has not come back on, even though I have made many trips, some up to 90 minutes at a time. While I fully expect the check engine light to return, I was hoping for an explanation as to why it would not immediately return, as opposed to this delay.

If the computer works normally in another E420, what are some of the other causes for this behavior? I believe that error code 19 suggests a fuel injector problem, but like I said, it seems to be running well in all respects.

Finally, the idle on the car seemed to be a little lower than normal (under 500 RPM), and it would very rarely stall at a stop light. I went ahead and used Redline Fuel System Cleaner on my last tank of gas, and it is now idles at about 700 rpm. I don't know if Redline would make such a difference or if this is simply a coincidence, or if, in my boundless optimism, a previously clogged fuel injector could have caused error 19 and the check engine light problem described above. I guess my real question is what is the normal idle speed for the 94 E420, and is there any adjustment? Thanks.