Hi my son has a 07 lacrosse with a 3.8. He stopped 2 get gas yesterday after started car pot in drive and engine just revved i went over and read the codes there was a catalyst code and acouple for accelerate pedal sensor and fuel pressure reg but none that i could tell for tranny. I checked fluid first it was less then half a qt low i don't believe enough to make allot of diff but Todd it off just the same. Car will accelerate in rev 2nd or 1st gears if shifts manually once you get sound 20 mph you can manually shift either from 2 nd to 3 rd or 2nd to drive n it shifts automatically up and down till you get down to sound 20 then you have to manually down shift to accelerate and. Any ideas?

Thank you

Unintended acceleration is very dangerous. Please do not drive it until inspections and proper repairs are made and all codes scanned again.
You are not alone.. Yeiks! Buick Lucerne general Vehicle Speed Control Problems
The culprit may obviously be a sticking throttle cable, butterfly, or entire throttle body itself.
Drive by wire cars, require the entire accelerator pedal replaced. The transmission will not shift correctly in this case without proper inputs.

Thx After i read codes i cleared them n drove short distance even tho car wouldn't accelerate from a stop in drive or 3rd and had to manually shift no codes came back

Hey Soft Ride, I think Slp4days is having transmission issues, not unintended acceleration . . . like as if the transaxle has a bad electrical connection.

Slp4days, check the electrical connection. If that looks good, you might need to scan it and see what it is thinking . . . like with a scanner that can read transmission codes etc.