Quote:
Originally Posted by PaleMelanesian
It could be that your engine management runs rich for a while after a restart or something like that, making the shorter eoc cycle at highway speed less beneficial.
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DING DING DING DING! We have a winner!
When you power back up, the ECU is programmed to wait for the O2 sensors to warm up. Newer cars have some logic to know how hot they are, but older ones just had fixed timers. 20 or 30 seconds of open loop could kill any savings you got shutting off the engine.