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Old 08-02-2013, 02:22 PM   #1
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Default Car accelerates by itself

Hi all,

I recently purchased a 2004 Chevy Impala 3.4L base with 68k miles on it and I am having a problem with the acceleration and coolant level.

About every other time I start the vehicle, the car accelerates on its own, to the point where I am riding the brake when driving on a level road. When the car is engaged in park, it seems to be idling high. Also, when the car does accelerate on its own, I can hear a high-pitched whistling coming from the engine.

The coolant level has been under the cold mark for the last few days. I have added approx. 1.5-2 quarts of Dex-cool. Today it stayed at the cold line and did not require more fluid. I was alerted to the problem because I could hear liquid flowing sounds coming from the dash.

Any advice on what I should do? I have brought it back to the dealer and he has been willing to work with me, but he was not able to replicate the acceleration problem.
The dealer did tell me that the lower intake gasket had been replaced recently. I took apart the air intake and cleaned the throttle body and the IAC, but it hasn't helped.

Thanks for any advice.
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Old 08-02-2013, 03:58 PM   #2
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Is this a high idle issue, or is the car actually accelerating?

Vacuum leak, faulty idle air control valve, and throttle position sensor are the first three that come to mind.
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Old 08-02-2013, 05:26 PM   #3
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The car is accelerating by itself, to the point where I need to ride the brake going straight.

I noticed the high idle when in park. The temperature also climbs to the 200-230 degrees range.
Vacuum leak sounds interesting. Would that also account for the high-pitch whistling noise I hear?
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Old 08-02-2013, 09:23 PM   #4
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Originally Posted by Chevy_Impala View Post
Vacuum leak sounds interesting. Would that also account for the high-pitch whistling noise I hear?

It sure would!
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Old 08-02-2013, 10:28 PM   #5
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on my old monte with that engine there was a black metal pipe that goes up and toward the tb from the water pump area. that developed a leak after a while were it makes the 90. worth a look but sounds like your thermostat is going or the fins of the rad and or condenser needs cleaned. best way is to remove the fans, spray from back with simple green and a hose a couple times.

as far as the acceleration i would imagine vacuum leak assuming the dealer knows what they are doing and checked the tps output. it would also be compounded by hot engine, all the rubber would be over expanding. you can test with carb cleaner run the engine and listen to it while spraying lines and gaskets and anything else
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Old 08-03-2013, 07:34 PM   #6
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my vote on the accel problem is the iac. when mine went bad the issue wasnt present but every few drives, but almost every time i went on a long trip, id go to pull off the highway and the car would stay at 75 all by itself.
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Old 08-16-2013, 11:15 AM   #7
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i would replace the iac or check for vacuum leaks.
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