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.

[avguy]

.... Their attempt at a solution was to charge me over $400 for a set of ignition wires and spark plugs. ....

High priced part hangers.

The Vent valve on my '05 stuck open, which set a large leak code. I bought a $5 vent valve from a U-pull, and that eliminated the code, and also passed emission inspection testing. IIRC, a new one was around $23, but it was easy for me to try a used one from a local yard, and it's still going strong. The is a very quick and easy DIY, and I'd just do that replacement first (given the specific code). And doing that may even take care of the hesitation as well.

[slayerized6]

My 2005 has a slight misfire on cold starts when its less than 30 degrees out. Once it warms up, all is fine. Ive changed just about everything and it still misfires until the engine is warmed up. Doesn;t bother me too much.

[moonrunner1972]

Folks, the replies are much appreciated. Can you specify where the part is you referenced?

[moonrunner1972]

Avguy,

Are you referring to the vapor canister purge valve?

[moonrunner1972]

Avguy,

Are you referring to the vapor canister purge valve, the vapor canister vent solenoid, or something different?

[avguy]

The vent solenoid is behind the rear passenger tire, connected to 2 small evap hoses - 1 to the canister and the other goes into a hidden trunk space. Might be easier if jacked up, but I didn't even bother doing that. Very quick and easy to replace that part.

Edit: yes, it's actually called the purge valve. Sorry for the confusion.

[moonrunner1972]

Avguy,

Thanks again for the timely advice and wisdom. I put the rear of the car up on jack stands to get a better view of the canister along with its associated hoses and valves. Although I didn't see any cracks or obvious damage due to the undercoating overspray , I started the car and sprayed the valve with starting fluid to listen to any changes in the tune of the engine. After about 10 seconds, the engine idle seemed to smooth out for roughly 30 seconds. Granted, this was the first start of the day so the ECM may have been running through its normal cycle. Still, the check engine light shut off and the car seems to run fine without any hesitation during sudden acceleration or moving from a stop.

Out of curiosity, I priced a new valve. Online, Auto Zone sells them for $34.99 before tax. Since the light is out, I informed my daughter to notify me if the light comes on again. I am considering the purchase and repair if the problem returns.

Also of note, I was interested to see that the lines are plastic rather than the fuel resistant rubber type of bygone eras. The hose located at the 9 o'clock position of the valve appears to have one of those odd looking clip fasteners where the one on the 2-3 o'clock position is of the spring clamp variety. During your repair, did you reuse the old clip (9 o'clock position) and how did you remove it? Thanks again.

[avguy]

Interesting that I don't remember undoing that clip at the back line, but not surprising. I don't tend to remember how any of these hundreds of different types of clips and connectors work, unless they give me a battle coming off.

When I removed the valve on my Aveo the metal clip on the other line was almost rusted out, and came apart in my hands. Then after sliding the valve out of the body clip, it turned out that the other line just pulled freely right out of the trunk port. It was not designed to be anchored, and just came out along with the valve. So I ended up being able to undo that clip after the valve was off the vehicle. It must have been one of those very simple and obvious push type latches because it came off without me even thinking about it.

Now I'll ask you a question about spraying the valve with starter fluid. I had initially planned to open up the old valve to try cleaning it. However, it was a completely sealed plastic unit, with no way to disassemble any part of it. So I'm curious how the fluid made it's way inside the valve. Did you pull the line coming from the canister and spray into that valve port?