CarTalk.com Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

2008 Chevy impala acceleration hesitation

I bought my 2008 Chevy impala maybe 6 months ago with 180k miles. Maybe after a week of driving it I had noticed the acceleration was off.

When i push down on the gas pedal from a stop the engine revs up normally. Once I get to about 35 mph the acceleration hesitation becomes noticable. With steady pressure on the gas pedal the rpm’s will jump up and down. When I try to put more pressure to the pedal there is always a serious delay until the pedal is at about 60% of the way down the engine will suddenly rev up to 2500 rpms.

I had done some research and thought that the problem was bad solenoids. I took the car into a transmission shop to have then look at it, but they had told me the transmission had no problems except for the trans fluid being a little burnt. They told me the problem was probably engine misfiring, so I replaced the spark plugs which had made the problem a little better but did not completely fix it.
I did more research and tried cleaning my mass airflow sensor and testing my tps sensor, but with no real results.

I was hoping someone with more experience might be able to help me diagnose this. I’m thinking it’s probably a bad sensor or some other electrical problem, but I’m not an expert.

P.S. thank you to anyone in advance for responding. I can also post a video if that will better explain the problem.

Is your check engine light on? If it is have them read at a parts store and post them here.

3 Likes

Maybe your fuel pump is starting to die. You could measure the fuel pressure to see.

You did replace that transmission fluid, I hope.

1 Like

There is no check engine light

I did not replace the transmission fluid, and I will check the fuel pump when I get a chance

Try cleaning the electronic throttle body,

image

Tester

Trans fluid that is “a little burnt” is sort of like the woman who says that she’s “a little bit pregnant”.

I really hope that you prioritize the trans fluid and filter change in the hope that you can avoid having to overhaul the transmission.

Any check engine lights? If not, it does sound like transmission slip from your description. You will likely need someone who has a decent scan tool.

Okay thanks, I am going to get the trans fluid changed asap

Thank you, I’ll try this when I get some time!

True story, food for thought (chicken feed? :baby_chick: ) …
This era of Impalas had some vehicles exhibiting “issues” with failing/failed accelerator pedal sensors. The pedal assembly actually has 2 (redundant) sensors and If one glitched there were problems with acceleration, not because the other sensor couldn’t handle it, but because it triggered a “limp mode” command.

However, I’ve not heard or read of any that did not set a Check Engine Light or put the vehicle in Limp mode, displaying “engine reduced power” type message.

Before GM extended the warranty on these pedal assemblies ( for safety reasons), my wife’s impala, from that era, had the symptoms described above. I diagnosed the problem (actually, the car did), and unplugged the gas pedal and plugged it in (took it right out and put it back, again, as it was easier for me). Voila! Problem solved (?) :slightly_smiling_face:. It never did that again and it’s ancient history, now. The pedal assembly was never replaced. Years later it’s going strong. Too bad I did that before the warranty extension was announced. Fretting corrosion, maybe? Salt water corrosion from melting parking lot slush in the frozen north? It makes me second guess the recall, but car companies can’t risk safety issues…

Anyhow, thought I’d throw that recollection out here. It was taking up some of my precious and limited remaining brain cells. :grimacing:
CSA
:palm_tree: :sunglasses: :palm_tree:

I agree with Tester; sounds like the throttle body needs to be cleaned. As for the “little burnt” transmission fluid I would have a bit more concern about that and wonder why the trans shop would seem to casually dismiss this.

You don’t suppose the trans shop was just trying to sell a trans service? Naw, that couldn’t be it!

What trans shop in the world would try and sell labor intensive service that’s possibly not necessary? [rhetorical question]
CSA
:palm_tree: :sunglasses: :palm_tree:

Have a bud, same car, same problem turned out to be the torque converter.

Thank you to everyone who’s trying to help me!

I checked the fuel pump and I don’t think that’s what’s causing my issue.
BUT, I did clean my throttle body and noticed a significant difference. The car has much more power and overall seems to run a lot better.

The throttle body cleaning had definitely made a difference, but didn’t completely fix the problem.

What I have noticed is that in 3rd gear is when the rpms seem sluggish. I will press harder on the gas pedal, but the engine acts like its stuck at 1200rpm.

The next thing I plan to test is the “accelerator pedal sensor”.

Thanks again for everyone helping me, and I’ll let you guys know if progress is made

1 Like