'eric' and 'jsap' -- Thanks for the advise. It appears that the 'switchover' valve is a simple electrically operated vacuum switch. I can easily work on electrical and vacuum systems. I did some more research and now pretty much understand the system. It injects air into the exhaust for up to 90 seconds once the engine is started and certain ambient temps are present. The oxygen causes the exhaust products to reduce until the catalytic converter heats up and can operate.
That's right. It's just to get the cats heated up. On other makes, this is usually called the smog pump, and it does operate during other conditions. I just don't know if this thing operates on our cars after warm-up. The Germans do things sometimes differently. For instance, my engine (which is a model year '97) doesn't have an EGR valve (but I think yours does), nor a PCV valve. Weird, but true. Just for info, the EGR wasn't necessary on my engine, and the PCV operates on crankcase pressure alone that reverses the breather tube direction of flow into the intake manifold....
Btw, I don't know for your car for certain, but it *might* have both a switchover valve (an electric solenoid) that eric mentioned (which on my car is a rectangular metal box about 1" x 3/4" x 1.5" with little tubes going in and out of it, but I don't know about yours) and a check valve (which, on my car, looks like a round saucer about a 1.5" diameter). First thing should be to make sure the plastic tubes and rubber vacuum connectors are not deteriorated, and to clean any clogged passages. Then replace solenoids and valves before investing in the actual AIP pump.
Again, get on the W163 forum as soon as you can. I can't help you much more on your car....
'jsap' -- I am having trouble accessing the Mercedes site "epc.startekinfo.com". I can access "startekinfo.com" but like you say --why pay big bucks when I'm not planning on making a habit of repairing Benzes. When I try the "epc ---" I get a "server not found" message. Am I doing something wrong?
Now, to help you get on epc....
Try this address:
(or, you can go "http://epc.startekinfo.com/epc/" and click on the "subscribe" link)
Click on "I agree" at the bottom of the screen. Then, it'll ask you for the credit card info, but it'll tell you that the 1 year subscription is $0.00.
After this, depending on your Windows firewall situation, you might have an easy time or a difficult time getting the Java app to run correctly.
Once you've successfully subscribed, but if you can't get the Java program to run correctly, let me know again, and I'll help you diagnose your firewall settings.
In the mean time, see the picture below to get a sense of what you'll get with the free epc subscription. It's a great resource, and it's the dealer gets the same info. The image will show you highlighted both the check valve (mechanical) and the switch-over solenoid (electronic) for my SL500. When you enter your VIN number into yours, you'll be able to find yours by navigating to Engine/Intake/AirPump.... You'll figure it out. Just don't give up on the stupid computer obstacles....
Also, here's a picture of your A.I.R. pump.