I started my 2005 dodge diesel with ether it idle alright then when I revved it up it stayed revved up at about 2300 rpms and up what's wrong

it sounds to me as if it is running too lean, check hoses for leaks

The one thing that can cause this is dirty or incorrect weight engine oil.

You need to take it in and have it scanned for fault codes, that is the first step in repair of this problem.

Automatic transmissions need to have a higher idle speed on the motor because of the load put on them by the transmission. You may have set it too low. 780 might be the idle speed with the transmission in D and the brake set.

It could be a vacuum leak but could also be a number of other thing's . Having the vehicle diagnosed by a qualified repair shop with the proper diagnostic procedures and equipment would be the way to go . Not guessing an replacing parts. That can be costly .
007 Idle Speed Problems Scan Data for Idle

Installing parts based on a code is not how it is done

The codes do not tell you what is wrong or what to replace

PO344-Camshaft Position Sensor Circuit Intermittent

The sensor just reported a fault code,now you need a shop
with trouble charts to properly diagnose the issue

Could be mechanical

02 sensors...Cat converter/s might be plugged

better take it to a local shop to get a digital readout of errors.....it could be transmission related

They are seperate issues, The gas cap code usaly means the vehical was fueled while running, Or cap is defective, The idle concern could be a vacume leak, Or a faulty idle air controll motor

BUICK RENDEZVOUS IDLES UP REALLY HIGH...WITHOUT PRESSING GAS. WHAT IS THIS?