I just fixed my 1998!!! The evap purge valve hangs on a vacuum line that comes from the charcoal canister. Just below the valve is a clear filter. The vacuum line between the filter and valve had started to fall apart on the inside and clogged up the valve.
I cleaned the valve with throttle body cleaner, any cleaner should work. Then tapped the valve on a shop rag to check the amount of dirt comming out. I was told the electrical connection on the valve is 12V, to open the valve. I suspect this may be true, but cleaning without opening worked for me. It is supposed to open when there is a lot of vacuum in the intake, which is why you only get the code when the engine is pulling vacuum at low rpms.

Klaus
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Just driving a 1998 V70R :)