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07 impala weird vibration/humming sound

1283 Views 1 Reply 2 Participants Last post by  Joes74challenger
My car has been acting very odd here lately and I can’t figure out why. I’ve noticed when using cruise control and when driving normally it will start to hum/a slight vibration as if it is losing power but it isn’t. If I push the gas pedal a little then it acts normal(no sound or vibration) until i let off the gas. If I cancel cruise or hit the brakes the noise/vibration goes away also

If I then resume cruise or accelerate the noise/vibration comes back. Some times it doesn’t. Also I’ve noticed if I just barely push the gas pedal at times, the car will vibrate and I’ll hear a slight hum and will act like it’s not getting enough fuel/power. This doesn’t happen every time but often enough. If I put the tranny into neutral, there is no hum or vibration so I’m wondering if it’s a tranny issue?

Ive replaced plugs and wires, air filter, and cleaned the throttle body. Also had a tranny flush done too. My local mechanic could not detect any codes with their scanner nor replicate what I just described when they had my car two weeks ago. I have noticed it more and more and am supposed to drive around with my mechanic this week to hopefully show them what I’m talking about. However if I can fix the issue myself I will.

I did have oreillys scan my car and I got code c0899. I have two air pressure sensors out but I don’t know anything about this code or if it could affect my problem above.

Just wondering what it could be? I’m going to clean all the electrical connections on the pedal and sensors. Has anyone else had an issue like this? What else can I check/do to fix this issue? Please help.
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on my 2010 3.5 i've found if it gets into overdrive at about 40-45 mph and you hit a small hill that doesn't cause a downshift the car will lug up the hill. you'll hear/feel a small vibration and as you stated it goes away as soon as the car down shifts by tapping brake, letting off the gas or giving it more gas to cause the downshift. i also noticed when i lived in Michigan it was always at a particular point of my drive to work. stop light before a slight hill that would always hit O/D about the time i hit the bottom of that hill. it drove me nuts!

what i figured out over time is that the car is programmed from the factory to get the best mpg's it can. so it tries to keep the car in the highest gear it can at all costs, which means it shifts into overdrive about 5 mph too soon causing that scenario. does this sound like what you were experiencing?

as for the code, someone who is much more experienced in troubleshooting will be of more service than I am.
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