2009 Other Chevrolet Models Engine bucks at 40 - 60 mph

Tiny
ZHANGMAN
  • MEMBER
  • 2009 CHEVROLET
  • 6 CYL
  • AWD
  • AUTOMATIC
  • 9,000 MILES
This is a 6-speed auto, and has two problems. Erratic I might add. Traveling at a steady speed and in 6th gear the car will "buck" a few times until I step on the accelerator a little more, then it is fine.
It also will hesitate to downshift to 5th at times.
All this comes about when the vehicle has been run steadily at highway speeds. Note, no problem until you require a downshift. It is not a fuel problem, that has been eliminated.
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Monday, August 24th, 2009 AT 1:23 PM

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Tiny
RASMATAZ
  • EXPERT
Dirty fuel injectors (cleaning the injectors often fixes this).
Bad MAP (manifold absolute pressure) sensor
Bad TPS (throttle position) sensor
Bad or dirty MAF (mass airflow) sensor
Low fuel pressure (leaky fuel pressure regulator or weak fuel pump)
Vacuum leaks (intake manifold, vacuum hoses, throttle body, EGR valve)
Bad gasoline (fuel contaminated with water or too much alcohol)

Sometimes, what feels like a hesitation is actually ignition misfire rather than lean misfire. The causes of ignition misfire may include:

Dirty or worn spark plugs
Bad plug wires
Weak ignition coil
Wet plug wires
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Monday, August 24th, 2009 AT 2:14 PM

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