Volvo Repair: 80/240dl starter will not disengage, brain twister, vacuum leak

Question
hello,
  my 80 240 wagon has about 200k miles.  about a month ago, it started stalling while driving but always started right back up.  i changed the spark plugs and the fuel filter. after this it seemed to do ok for about two weeks and then one day it started shaking and sputtering on me and then just died in the middle of the street.  i tried 3 more times (in the middle of the street) to start it back up and on the third time, it started shaking and it sounded like i was trying to start the car with the ignition already running.  i immediatly turned it off and pulled the key out but it just kept going!
   ever since then, when i try to start it, this same exact thing occurs.  the only way i can get it to turn off is by pulling off one of the battery cables.  i am completely baffled.  i have some mechanical knowledge (thanks to the "trusty" wagon)  is there any way you can give me a jumping off point?  i would appreciate any suggestions.  thank you
amanda

Answer
Hi Amanda,
          Wow what a brain twister..
          You seem to have 2 or more problems.
         The reason your car runs lousy is caused by at least a dozen possible causes.I'll try to cover a few...you may have a vacuum leak..leaky coldstart valve..
failed fuel componant.problem with fuel dist.or related parts...Dirty electrial connection...possible problem with fuel pick-up in fuel tank pump..vacuum hose fell off connection..
         NEVER disconnect battery to shut off engine...you WILL toast your alternator...disconnect coil connections instead..
          I'm at a loss to figure out why the engine runs on w/o key...the alternator does have a connection to the ignition...maybe a problm with alt...carefully disconnect alternator wiring...run car...shut it off...if it stops running on...your alternator has diode failure..a real low battery voltage does weird stuff to running engines.This car requires a expert to assess its needs...if you dont want to spend 100's on finding the answer...search out a competant Volvo mechanic and use his knowlege to save yourself lots of loss'.
                      Good luck,
                              Bilbo

you changed fuel filter?...super lousy job...better off paying someone else to do this job...(fuel filter under car mid section).`