I have a 99 5.2l that i just replaced the battery in because the arizona heat is death for batteries. and mine died earlier this morning at school. ran fine on the way to school this morning had no issues. went to go move it to another parking lot closer to my next class and it was as dead as can be. couple hours later after class got it jump started and made it home, on the 25 mile drive home from school however i was going 70 on the freeway the whole time and idle was at 2k, foot off gas and it dropped quickly to 1.5k then to 1.7k, gas it up and it would stay at 2k. swapped out batteries for a brand new duralast gold from autozone. got the battery in and it didnt start, finally after a few minutes got it to start. once started i had no idle whatsoever, foot off gas and it wouldnt stay running. went out after a couple hours to see if maybe it just needed a break, and it wouldnt even crank over...anyone that can help diagnose this issue would be great. thanks

 

Sounds like you have a connection to your battery that is bad. Clean the posts and terminals at the battery and try to start it. The next thing if it isn't battery or cables then clean the throttle body and IAC.

 

check the starter relay, also check for shorts in the system

 

Sounds like bad terminal connections. Clean the connections like new and update.