Assuming it's the correct airflow meter, it could be an intermittent bad electrical connection or an air leak after the meter.  Check the plug and all the contacts to make sure none have spread, causing a poor connection.  Have a good look at any other plugs you might have disturbed while fitting the meter as well.  Then make sure the trunking is fitted properly and tightly to the meter and also take a look at all the breather pipes from the engine - if they are disturbed, it can result in a leak.  A poorly fitted pipe will allow air into the inlet manifold that hasn't been measured by the meter, so the system will not inject the right amount of fuel.  Of course, it could be entirely unrelated to the new unit.  Why did you fit it in the first place - what were the symptoms? 

Tim