2000 Silverado starting to idle fast

[RLEE]

I have a 2000 Silverado with 5 speed and the small v8 (4.7 I think)  125000 miles. I drove for 7 hours straight on the high way and when I pulled of at my exit the motor and rpm were still running pretty high. ( well over 2000 rpms).  So I cut it off and restart it and it acts normal again. 

This same thing has happened twice on long trips cruising 70-80 mph for long periods of time.  And now sometimes during daily driving around town , I notice the rpms sitting around 1000 . Which is a little higher than normal .  

Check engine lights been on for a long time. (The truck sit for 2 years before I put it back on the road) 

will I need to see a dealer to read the codes? 

I see autozones offers to do it for free on their commercials. 

If anyone has any ideas what the problem is I’d really appreciate it. 

[Coby7]

Leaky intake gasket.

[RLEE]

Thank you for replying. Now I have a place to start.  After I find a mechanic I will update this thread