I looked it up and it said "target idle not reached". The dealer said something about a vacuum line. Where is it and how do I fix it?

 

what yr is your truck and what engine does it have?

 

It is an '02 RAM 1500 QC SLT 4x4 with a 4.7 ... Any help is much appriciated.

 

Your dealer was probably assuming that the code was caused by a vacuum leak, so it could be any vacuum line.
That code can occur when there is a vacuum leak that makes the air/fuel mixture lean, so the ECM adds more fuel, but that makes the idle go too fast.