Hey,

I was wondering if anyone has a general idea about how long it takes the
ECU to 'learn' to its greatest potential. I'm not sure of the best way
to frame this question, but it relates to my observations of my '91 Si's
engine speed relative to the car's speed.

When I go on highway trips I'm aware of my engine speed at various
cruising speeds on flat stretches. For example, my car will usually run
~ 3200 RPM at ~64 mph, but just yeaterday it was closer to ~3000 RPM at
~64 mph. The last time I disconnected the battery was less than 1,000
miles ago, and less than 4 months ago. The ambient temperature yesterday
was above freezing (warmer than usual).

For more perspective, the car has ~ 140k miles on it, with stock (for
Si) tires/rims. Is part of this the age of the car, and perhaps
fluctuations in the output of sensors due to their age?

Mark