2001 Pontiac Grand Am shakes while at idle

2001 PONTIAC GRAND AM
100,000 MILES • 4 CYL • FWD • AUTOMATIC
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WILLIAM8321
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  • 1 POST
I am working on a 2001 Pontiac Grand Am GT with a 2.4L engine. When the car is idling, the car feels like its shakeing. It also seems to idle rough. Ive already replace the spark plugs and boots. I also checked to see if the coils were firing and for primary and secondary resistance, all are good. I also replaced a few cracked vaccumn hoses that were cracked. The check engine light is not on.
Dec 31, 2009 at 10:00 PM
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RASMATAZ
  • ✓Experienced Mechanic
  • 75,992 POSTS
A rough idle or misfiring could be caused by a large vacuum leak that can lean the air/fuel mixture out to such an extent that an engine will not idle at all. An EGR valve that is stuck open at idle can have the same effect as a vacuum leak. So too can a loose positive crankcase ventilation (PCV) hose, a leaky PCV valve or the wrong PCV valve (one that flows too much air for the application). If somebody replaced the PCV valve recently, they may have installed the wrong PCV valve. The rough idle in all of these cases is caused by "lean misfire." The fuel mixture is too lean to ignite reliably so it often misfires and fails to ignite at all. Lean misfire will show up as elevated hydrocarbon (HC) readings in the exhaust, which may be enough to cause a vehicle to fail an emissions test.
Dec 31, 2009 at 10:10 PM
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