HouseCallAuto 8/7/2010Codes do not come up immediately because the computer uses two trip detection logic meaning if it sees the same malfunction in two consecutive drive cycles it turns the light on and / or sets the code. It is never immediately. The valve you replaced under the washer tank is the switch over valve although you referred to it as the "purge valve". There is another valve called a "purge valve" as I see it in schematics but have no location for it. Check the wire circuit as I described for that valve above in previous answer.
vince^_^ 8/6/2010Check the condition of your vacuum and hoses, it may have a leak.
MARIO 8/6/2010If there was a leak, wouldn't the check engine light come on immediately rather than after diving 10 miles? Is the same code. Can the new part be bad? Anything else?
HouseCallAuto 8/6/2010Seems there is another part called a purge-flow switch over valve that could also be bad. It is connected indirectly to the purge valve which you changed already. I have no specific knowledge of MB diagnostics of this specific system but after reviewing a schematic my advice would be to check the electrical connections to these two valves. Specifically, the purge valve that you replaced has two wires and the black / yellow should have battery voltage with key on. If not, check fuse #30 (15 amp). The other wire is for the computer to turn the purge valve on (computer sends a ground - and this ground will only be present when the valve is called upon to function)
The other valve (which you did not consider) is the purge flow switch-over valve. Most likely a bad valve OR a broken vacuum line at the valve. Valve is located UNDER the w/s washer reservoir.