My 2003 chevy impala idle high in park n when i put it in drive it will go up to 40mph without being on the gas pedal

Take it to a repair shop

No one can guess at all the possible
problems it may have

Unless you work on your own vehicles &
provide test results & have a specific questions,
we can't do much for you

vacuum leaks .. high idle solenoid messed up..works with the defrost setting..

Back to the mechanic - sounds like either an IAC motor or TPS sensor is the problem, but also could be the throttle cable (sticking leaving the throttle not fully closed).

A temp sensor out of range giving a false cold reading can cause high idle . A MAP sensor can also cause high idle by advancing the timing resulting in higher idle .

(Not a mechanic) First thing to check is the transmission fluid level. If excessivly low it may not move. (Usually check trans fluid with transmission dip stick, while engine is idling and warmed up) Consult owners manual to verify procedure. If your fluid levels are normal or close to normal, you should call a transmission shop unless you are or know a good mechanic.

Sounds like the Throttle Position sensor or the Idle Air Control Valve causing the issue

check the engine breather pipe if its split or perished it will cause this ,if its ok then its a new idle control valve or it may just need a clean

007 Idle Speed Problems Scan Data for Idle Hooking up a scan tool that can view engine sensor data is the way to find these type problems .

If your idle is going from 500rpms to 1000rpm's fluctuating at and idle your EGR valve is probably carbon up and needs cleaned or replace.

Throttle position sensor. It's under recall for most Malibu models.