This could be an airleak after the airflow meter, any freshen dragged in here isn t seen by the ECU and thus not compensated for and can lean the engine out and can also permit the engine to rev in the works taking into account not desired causing harsh running. As its a mechanical idiosyncrasy it tends not to face upon the anomaly blithe and you can sometimes listen a hissing noise bearing in mind the engine running.
Its along with worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a not at your best pump will all upshot in insufficient fuel brute delivered to the engine. Might furthermore be worth cleaning out the idle eagerness control motor / valve as these get clogged going on similar to carbon and some brake cleaner washed through helps release things off.
This could be a large vacuum leak ,with the MAF connected it is solitary measuring the air that is getting next the MAF, therefore if the intake manifold is sucking in expose the ventilate to fuel ratio will be unquestionably out and cause the engine to stall. If MAF is disconnected the engine goes into a limp measurement and lets the engine run. afterward carb cleaner spray spray can in the area of the hissing past the engine supervision and bearing in mind you hear the engine stall or rev superior there is the leak ,could be a bad vacuum hose bad gasket on the manifold.