Gretchen
Black exhaust is usually indicative of a too rich condition.  Surging can result, as well.   One possible cause would be a faulty thermostat.   Mine evidently got old and weak and would open prematurely and get stuck in the open position.  This would allow cold water from the radiator to flow around the coolant temp sensor for fuel injection quantity.  The sensor would think the engine was cold and dump in more fuel, when in reality the engine was warm.
Maybe, just maybe,  your thermostat got fouled with gunk while sitting up for a month.  This is only one possible cause.  
If it does it again, observe your coolant temp gauge on the dash.  Mine would dive to the cold side when the too rich condition occured.   A new thermostat saved the day and a Thanksgiving trip to Nags Head, NC.

Hope yours is a simple fix.
Dan Hall
"Das Boot"
86 Wolfsburg(poptop-no kitchen)

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From:   Lee Tucker[SMTP:tucker@SPIRITONE.COM]
Sent:   Monday, February 22, 1999 10:29 AM
To:     vanagon@GERRY.VANAGON.COM
Subject:        black smoke

Our 86 vanagon (which had not been driven in over a month) was blowing
out black exhaust.  I also experienced power surges.  Both problems
seemed to go away after a while.  What are the possible causes of this?
Please reply to me as well as the list.  TIA
Gretchen