Start by checking the cable running from the gas pedal to the throttle body---make sure its not binding. Possible issues would include an accidental bending or kinking of that cable although your symptoms suggest this happens just once during each drive cycle.
Disconnect that cable from the throttle body, actuate the TB by hand to make sure its not "hanging up", that it moves freely both opening and closing.
With the cable detached check to pedal's operation to make sure something inside the cabin hasn't become lodged somewhere in its pivots etc.
The accelerator pedal system is fairly simple, pretty much maintenance free for the most part----this is certainly an odd situation. Best part is nothing is too expensive should replacement parts be needed.
Please let us know what you find---for our mental data bases.
SilVan
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