Mine was predominantly at idle, but occasionally also at 3-3500 rpm.no cranking issues.
My advice to you would be
1) check ignition timing-often a cause of idle misfire.
2) check all ignition components. Plugs, leads, rotor and dizzy cap. Also pull your ignition coil and test it with a multimeter. It cranking for a while would make me think it wad ignition related- but i could be wrong!
3) lambda sensor is a common cause of idle misfire. In a lot of cases, malfunctioning components won't always cause the ecu to store a fault code, which can throw you off the right course of action to take-this is particularly true of the lambda. A faulty lambda may also cause your engine to run rich or lean-check the plugs to confirm either situation.
4) its also possible that your throttle position sensor could be at fault. Very easy to do with some feeler gauges and a.multimeter.
Other possible causes-fueling issue such a failing pump or lack of fuel pressure, though that would be very obvious-struggling to accelerate or get up a hill etc.
compression issues can be a cause as well as vacuum leaks.
Go with the first 4 points to start with. They are all easy to check yourself, just get yourself a multimeter and refer to the bgb.
If ya need any help just ask
