Join Date: Feb 2017
Location: St. Louis, Missouri
Fuel injected engines in general stop injection during decel until rpm approaches 200-400 rpm of idle speed. This is done as an emission control measure, and also as a fuel economy aid.
I've watched injection patterns on labscopes and viewed a base pattern that looks like a lower-case "r", acceleration and the top of the "r" elongates as the injector duration(time in milliseconds the injector is held open by the engine control unit)increases, chop the throttle and the pattern disappears until rpm approaches base idle speed.
Some engines with secondary throttle plates vary their opening and closing angles to adjust engine vacuum on decel. In a discussion with the Suzuki factory service rep earlier this year he said that one of the changes in programming for the '14-'15 DL1000 ECU recall was to open the secondaries to soften engine braking during decel.