senses. There is a failsafe in case the MAF goes bad (or is unplugged) so that the car will still run w/o a working MAF, albeit less efficiently. By unplugging the MAF you are just putting the car into that failsafe mode. If the MAF is working, as I suspect it is, but your air, either intake or via vacuum, is leaky, the "good" MAF data will cause the car to run poorly because what is measured by the MAF does not reflect what is actually going into the engine.

Check again for an intake hose crack between the MAF and the throttle body. Also disconnect one of the vacuum hoses while the car is running to see if things change, and/or spray some carb cleaner around the intake area, but not directly into the intake, while the car is running to see if it helps you locate the leak. For giggles you can even remove the intake hose behind the MAF entirely, so you _know_ there's a problem, and disconnect the MAF as well and see if it still runs.