I just ran the fault codes and got this:

18010 power supply Terminal 30 - P1602 (voltage low)
17967 - Throttle Body - P1559 (fault in basic settings)
18032 - MIL request signal active (check TCM for errors!)
17973 - Throttle Actuator (J338) - P1565 (lower stop not reached)
16486 - MAF Sensor (G70), P0102 (signal low)

Anyone have any ideas? I don't see anything glaring at me from the throttle body; I haven't touched the accelerator (which is where I think the actuator is)

I do have what appears to be a vacuum line that goes to nothing and I can't figure out where (pic below) - could this be a line that needs to go to the throttle body somewhere?

(the yellow line is my drawing so you know which line I'm talking about)

 

it sounds exactly like a problem i had withadn old police cruiser.... it turned out to be running off of vacuum instead of actually running the fuel pump....
the car acted like new until the accellerator pedal was used while in gear....
what was happening?
while the injectors were actuating the engine vacuum was allowed to suck the fuel from the tank but the fuel pump was not running after the initial 3 seconds of priming when the key was turned on ....

weirdest bad fuel pump i'd seen before.... the customer drove it 50 miles to my shop with no fuel pump.... (he'd let it idle to around 25 before he would quickly pulse the throttle repeatedly to get it to rev up and then set the cruise control to make it to me.. )
not saying that you're having the same problem but it is worth the time to put a test light on the pump while you drive and see if the pump is even trying to run while you're in gear....