This will probably be too long but just want everyone to have the information. Seems like I have fixed my problem. I replaced the air flow sensor (from Fast Lane) and it now seems almost back to where it was. I say almost because it seems like in the "limp mode" it had a little more acceleration off the line but that might be my imagination. Maybe an extra rich mixture and not meeting emissions in this mode? There also seems to be slight differences in the driving of the car. I cannot quite explain them but evidently the sensor has not been quite right for some time. Anyway, no more check engine light, no more fault codes.

Regressing a bit, after my last post, for some reason I cannot explain, I tried starting the car with the air flow sensor disconnected. The car ran exactly the same as with it connected. At that time, I decided it must be bad. I could not believe how well the car performed (except at idle as I have described before). Started properly, drove nicely, no loss of power. Just would not idle properly. If this is a "limp mode", I hope to have this type when I get to be 90 years old!

Before doing the air flow meter, I did put in an over voltage protection relay and it was exactly as I expected–no change at all. But now I have a spare for what I understand is a troublesome item.

As far as I can see, the insulation on my wiring is good. I can find no indication of any flaking or cracking of my wires. However, the plastic locking mechanisms on some of the smaller connectors seem to crack and fall off when I try to take a connector off around the engine.

As far as the fault codes for pre-OBDII Mercedes, I found a site that seems to give most of them. The years for the different models seems a little mixed up but you can figure it out by looking at the engine size. The site is:

http://www.batauto.com/MB.html

It also has codes for a lot of other cars as well. Go to:

http://www.batauto.com/technical.html

Thanks for everyone's help. I think this information exchange is terrific. And thanks to Fast Lane for very reasonable prices. I also got a new headlight at a price I thought was unbelievably low. (Just the old original equipment–hardly ever drive the car outside the city limits or at night.)