Intermittent Hesitation

[moonrunner1972]

Good Afternoon all! I am in need of some advice regarding my daughter's 2004 Chevy Aveo. The car is experiencing an intermittent hesitation upon acceleration. I was finally able to recreate the problem after a franchised auto repair shop failed to correctly diagnose the problem. Their attempt at a solution was to charge me over $400 for a set of ignition wires and spark plugs. This of course failed to correct the problem.

My daughter noted that the problem most often occurs when the car is cold and turning left. Also, the check engine light is illuminated. The Auto Zone scanner displays code # P2422, PCM detected the evaporative emission system vent vacuum. After replacing the fuel cap, the codes were cleared but within 48 hours the light is on again.

I am taking it to have the code read again but I am hoping someone has experienced a similar problem. Any help is greatly appreciated.

**********************************UPDATE********** ****************************
After a second scan, the scanner displays the code # P0455: The ECM has detected a large leak in the EVAP system during a system monitor test.

Possible Causes:

1. Defective, loose, or missing fuel cap
2. EVAP canister broke, hose cracked or not connected
3. Purge or vent solenoid defective
4. Vacuum leak at engine

In addition, my daughter informed me of a thump sound similar to that of a heavy item falling inside the trunk area. Initially I discounted this as a symptom of the brake problem I repaired. After hearing the same sound post brake job, I assumed it was a result of something done wrong. However, I asked if the sound occurred when the car is stationary which in fact it does occur when stopped and when moving. Therefore, I am going to trace all vacuum lines from the fuel tank/charcoal canister forward to the engine compartment. Again, any advice, tips, personal experiences are welcomed and greatly appreciated.