Hey everyone out there im having a problem with my monte carlo i change my starter on it and now it starts and stop but if i hold the key a couple of seconds it runs for a lil while then shuts off i changed the ignition switch and the crankshaft sensor

 

Can you give a few more details?
I got the part that you put in a new Starter and now it starts up,
and it must shut off as well?

I am not sure why you are holding the key? When I start mine I let go of the key and no issue's.
who What or Why does it shut off?
Did the Switch or the sensor help?

One thing to check is the Vacuum line that runs from the engine up to the fire wall behind the brake master cylinder if that gets disconnected it will give you fits.