no disrespect to your friend but was ther pulse measured correctly and do you actually have a problem with injector at all?
the sudden increase to 1500 rpm is significant as it can be caused by a number of things which in turn can be the cause of your misfire
assuming your engine is idleing on 4 cylinders ok
try this for a few simple pointers
start your engine let it run at 1500rpm,disconnect the plug pluged into the idle speed control valve its the silver cylinder mounted into the throttle body held in by 2 screws,after doing that your revs should drop down to base setting,if not you may have an air leak after the throttle valve like a hose or a dump valve diaphram,manifold gasket,loose manifold bolts etc etc,
depending on the above it could mean a simple fix or a bit more trouble shooting as a sensor may be out of adjustment or failed.but nothing to worry about its all fixable
maybe stu has more to add