Probably a bad throttle position sensor. If cycling the accelerator pedal up and down without the engine running 50-75 times changes the symptoms when you start the engine, odds are very good the TPS is bad and needs replacing. You can do the same thing more easily by cycling the throttle linkage on the throttle body. Cycling the throttle works the TPS wiper (it's a variable resistor) inside back and forth which may clean it up temporarily enough inside to make it work better... which also indicates it needs changing.
If doing that changes nothing, it doesn't necessarily indicate the TPS is good either. The TPS is just a common cause of such issues. If it goes bad, it can't be cleaned, only replaced.