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RPM fluctuate after letting off gas(coasting)

RPM fluctuate after letting off gas(coasting)

 
Old 08-19-2018, 04:01 PM
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Default RPM fluctuate after letting off gas(coasting)

hey, all members of Audi world forum. I am new for this forum. recently a tragedy happened to me. the story and the main problem of the car are described below. If you guys have any idea, pls help and let me know. thank you in advance. have a wonderful day. MY car is 2010 audi s5, 70000 mile

recently, the check engine light appears on the dashboard, which is about intake running tunning(runner control). since my car is running well, i though there is the minor problem, i have my car repaired in the local auto shop instead of the dealership. but that incompetent mechanic fail to repair my properly(i think he mis install the component). when I pick up the car from them and drive it on the highway. there is loud noise coming from the engine and the car was shaking. so i send my back to them and they fix it in the next day. they told me there is no problem when I test drive my car. I only can feel there is little difference but not the noticeable problem( no check engine light, gearbox light) so i just let it go.

after driving 500 miles later, the car has mainly suffered two problems:
Abnormal Coasting (only happened after letting off the gas pedal), i have recorded it and post it in youtube, PLS CHECK IT:

When my car is running on high way, I hit the accelerator to 2900 RPM and then let off the gas to let my car coast. the rev drops and then FLUCTUATE couple time.

meanwhile, I can hear noise "emememme" coming from (catalytic converter or transmission). When sound is there, the car is slow down QUICKLY (feel like harsh downshifting) as If I was pressing the brake lightly but I did not . 1 or 2 second late, When sound is gone. The car is coasting as the NORMAL, the car is slowing down GRADUALLY (normal)


Each time, when coming to stop, the RPM needle jump one time then decrease to normal idle speed.


Only happen one time.

when my car is running on the downhill(really sharpe). Again I let off the gas and let the car coast. The rev is stuck in 2000 RPM(gear is stuck??). The brake is stick. At that time, there is sound like emememememem!!!!. I have to hit the accelerator again. rev goes up. Then I hit the brake , my car slow down and the rev goes down.




the second problem is my car is hard to accelerate (not noticeable problem)
When the engine is cold, when i drive my car out of the garage, I hit the accelerator, it is easy to accelerate and get about 4000 rpm. But right now, it is hard to go over 3000 rpm.
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