2003 4.6 running rough at idle and then was stalling. Checked and found the rubber elbow on the vacuum line from valve cover to back of intake was almost in half. Replaced the elbow and it runs fine in park but when I put it in drive with the air on, the RPM's drop to 500 and stalls occasionally. When I turn off the air it idles ok, but runs a little rough. My question is, since the elbow has probably been cracked for quite some time, does the computer need to re-learn the change?

 

I would reccomend you remove the IAC and spray clean it's inside making sure the slide valve moves.
At the same time remove the air hose off the throttle body and spray clean inside all around the throttle plate.
After reassembly, remove one battery cable for about 2 minutes then reconnect.
Start the motor 'cold', turn on the A/C, lights and fan.
Let run to fully warm then drive about 5 miles out and back.
Do several hot restarts.
This should relearn nearly all that is needed and be perfect starts providing there are no other faults.
Your problem now is the IAC is not reacting to the A/C load and bogs the motor down because it cannot add air to keep the idle stable at 750 rpm hot.
Good luck.

 

Thanks Bluegrass, I will get on it when the sun comes up!

 

Got into this morning and did what you said Bluegrass 7. Running great now and "service engine soon" light went out. Thank you for your help, this site rules!

 

Your quite welcome.
The system operation is quite involved for the average owner to understand.
So much for full computer control.
Good luck.