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You need to take into account the energy regained on the compression stroke, even if we assume constant pressure and all to make things simpler.
2042rpm is 2042/60=34.03 revolutions per second. The engine draws in half its rated displacement per revolution, so this is 1.905L * 17.01 (let's just drop the thousandths) = 32.3L/second.
The intake stroke consumes 32.3L*42.8kPa=1382 J per second, or 1.85hp. I don't know where your 36hp is coming from.
To sweeten the deal, the compression stroke now regains some of that power, probably around 40% of it. So the total loss is about 1hp. Seems about right for a 1.9L engine that runs at those speeds.
BMW only saw 10% improvement in fuel economy on naturally aspirated engines with Valvetronic, the throttle is not as evil as some people make it out to be.
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