A sticking choke or vacuum leak are two common causes.
Idle speed too high.
Idle is controlled by the ECM (computer). Not adjustable. check sensors
Where is idle air control valve located on 2003 Pontiac Grand Prix GT, 3.8 liter 6 cylinder?
The 2000 Pontiac Grand Am engine idle vacuum hose is located on the back of the injector fuel pump. A diagram of the vacuum hoses can be obtained from most General Motors dealerships.
the choke is on
Why does my 2000 Pontiac Grand Am, with a 2.4L engine, run rough at idle but runs normally when placed in neutral? I changed the plugs and air filter, but the problem continues.
idle air control motor.
The cause of high engine idle and surges in the 1989 Corvette is due to..Read More
possibly on of the belt pulleys or a vaccum leak
Pontiac 1993 vehicles have been known to have Fuel Pressure Regulators that when they fail, they will release too much fuel to the intake and therefore produce erratic or Idle up and down. Also, the erratic Idle can be caused by a air pressure leak located as part of the Emissions system.