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Chevrolet Repair/Acceleration issue

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Question
Hello,
I have a 2004 Chevy impala LS 3.8 with about 150K miles. If I am at a stop light or at a dead stop and then I accelerate to take off the car will jerk. I am not sure whether to describe it as a jerk, a hesitation, or a slip. When it happens I always immediately take my foot off the peddle and then I reapply my foot to the peddle to give it more gas. When I do that, the car accelerates fine. This has been happening on and off since January of 2010. It is happening more frequently now and the other day the "jerk" was quite intense. It only happens after I have been driving for a while and the car has had a chance to warm up. I have not paid attention to the RPM’s when this occurs because it always happens when I need to be watching where I am going. LOL

Some other issues I am having with the car (which may or may not be related to this or causing this) are as follows:
1)   I get an engine code of P0455. I have been getting this code since June 2009. I replaced the fuel filter in November 2008, the evaporation solenoid in July 2009 and the thermostat and throttle body gasket in May 2013. My air filter is fine. At this time my mechanic mentioned there is a little coolant getting passed the head gaskets.
2)   The engine is running slightly hotter than normal. The temperature gauge after the car is warmed up runs at the highway mark (never goes higher) where as it used to run a hair lower than that. The car’s fuel efficiency has also slightly decreased. I put on 150 miles a day going to work and I monitor my gas mileage so I know it has decreased.
I really appreciate any input!

Maddy

Answer
HI MADDY,I WILL START OUT WITH THE PO455 CODE. THIS WILL HAVE NO BEARING ON THE WAY THE CAR RUNS. THIS IS FOR A LARGE EVAP LEAK IN THE FUEL SYSTEM..VAPOP LEAK NOT RAW GAS..THIS WILL NEED TO BE TAKING CARE OF IF YOUR STATE DOES EMISSION TESTING..WILL NEED TO PUT SMOKE IN THE EVAP SYSTEM TO FIND THE LEAK..IF YOUR ENGINE IS STARTING TO HAVE HEAD GAKET LEAKS I WOULD ADDRESS THIS SOONER RATHER THEN LATE. THIS WILL MAKE THE ENGINE RUN HOTTER THEN NORMAL AS WELL.THIS WILL ONLY GET WORSE..AS FOR THE RUNNING ISSUE THIS COULD BE FROM A FEW THINGS, MASS AIR FLOW SENSOR,TPS SENSOR[THROTTLE POSTIONING SENSOR]AND LAST IS A FAULTY THROTTLE BODY UNIT..THIS WILL NEED TO BE TAKEN TO THE CHEVY DEALER OR A SHOP THAT HAS GM SOFTWARE TO RUN A DATA SCAN [NOT JUST CODES] ON THE PCM [POWER CONTROL MODULE] TO DIAGNOSE THIS PROBLEM CORRECTLY..WITHOUT THIS I AND YOU WILL ONLY BE GUESSING.I WISH I COULD BE OF MORE HELP BUT THIS IS SOMETHING I WOULD REALLY NEED TO DIAGNOSE IN PERSON.....GOOD LUCK TO YOU,,,TOM.....

Chevrolet Repair

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TOM SHEETS

Expertise

PLEASE READ ALL OF THIS BEFORE ASKING ANY QUESTIONS. IF THIS CHEVY SECTION IS MAXED OUT.YOU CAN REACH ME IN THE OLDS/BUICK SECTION. Will answer questions from 6:00am to 10:00pm all days [EST][[[ NO DIESEL OR PAINT QUESTIONS]]] will answer all 1965 to present QUESTIONS ON ALL GM'S on mechanics of these cars. Keep in mind i am not there in person i am going on what you are telling me !! PLEASE IF ASKING A QUESTION GIVE ME AS MUCH INFO AS POSSIBLE. THE MORE THE BETTER. SUCH AS YEAR,MAKE,MODEL,ENGINE SIZE. THIS WILL HELP ME HELP YOU. I will not be able to answer all questions because of some situations that i would really need to be there and see things for myself,such as electrical issues. In many cases i would need wiring diagrams. I can also give you an estimate on what the cost would be at our repair shop as an idea to help you. Keep in mind that my answer is ONLY MY ADVICE,ck with your mechanic as well.. >> THANK YOU, TOM..

Experience

I have been a ASE certified master mechanic for over 30 years and certified IN ALL 8 CATEGORIES,[engine repair,engine performance,auto trans,manual trans,clutches,steering and suspension,brakes,electrical systems,heating and air/cond. I am also a state CERTIFIED inspector for over 30 years. I do computer work [pcm]fault codes,pcm flashing,state inspection monitor readiness,repairs on exhaust,fuel service,[injection and carburetor,] charging system problems, running issues,alignments,frame problems,tire balance,struts and of course standard and anti-lock brakes.

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nys state auto repair industry and ase group.

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N/A

Education/Credentials
high school,4 years of tech school,and many many hours of auto training with many gm classes and aftermarket training classes..

Awards and Honors
ASE MASTER TECH CERTIFIED IN ALL 8 CATEGORIES.NYS INSP LICENSE AND A/C CERTIFIED

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MANY CUSTOMERS IN OUR BUSY SHOP.

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