Hello and welcome to JustAnswer!
Does the check engine light come on?
Let's see what codes are stored. Cycle the key from off to on three times ending with it on and watch the digital odometer display. Don't crank the starter, just off to on. The codes start with a P and have four numbers, there may be more than one stored. Write down any that you see and post them here.
You can press the trip odometer reset to temporarily turn off the gas cap warning if it's interfering with checking for codes.
Did you get an owner's manual with the car? It's sounding like the manual might be missing. You can download it HERE if you don't have one.
It will go away when the powertrain control module sees the problem is gone for three good trips. After the problem is repaired it will take about three days of regular driving to no longer see the warning.
From AutoZone troubleshooting PO457:
aaEvap small leak detected: explanation-The ECM has detected a large leak in the EVAP system during a system monitor test.
aa1-Defective, loose, or missing fuel cap
aa2-EVAP canister broke, hose cracked or not connected
aa3-Purge or vent solenoiod defective
aa4-Vacuum leak at engine.
I loosened and tightened the gas cap with the engine running, drove four miles to work, shut it off. Came out ten minutes later and the gascap and engine light did not come on. Drove another four miles to AutoZone and there were no more service notices. Above is the printout for the troubleshooting test.
It sounds like the gas cap issue is worked out then.
You mentioned having to hold the brake or the car will roll forward. What is the idle speed at when this happens?
There's no need to relist the question, you simply need to hit the reply button to respond to me. I can't be there to feel or diagnose the problem in person so I have to rely on information that I receive from you through asking questions.
The fault code had set because you or someone at the dealer left the fuel cap loose, and it's not related to an idle problem.
No, this isn't a symptom of a failing timing belt, and yes you will need to replace the timing belt in the future. The timing belt has a service interval of 100,000 miles.
Back to the last question I was asking, what is the idle speed at that you think it's too high?