I parked my car yesterday and was straightening the tires when I saw my RPM go up from about 700 to 1000. Why does it do this?
In: Engineering
There’s a few possibilities here.
First, when you shift into Park the transmission effectively goes into Neutral. That means that the weight of the (not moving) car is taken off the (spinning) engine and the reduced load will make the RPMs increase for a moment before the engine control computer realizes and reduces fuel flow.
Second, especially in older cars, power steering is powered by a pump which runs directly off the engine from one of the belts. Turning the wheels adds requires pump pressure which is a bit of engine load, and when you finish the load on the engine is reduced causing the speed to spike back up for a split second.
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