A vacuum leak can cause that.
what is the down side of the 1997 buick park avenue
Look for a vacuum leak. Could be anywhere.
Please be more specific ....what is an "idle air motor"...I have 25 years experience and have never heard of it???
Most likely, the alternator is going out. It puts out more at higher RPM's, so it would charge more going down the road than it would at idle. Good Luck!!!
A Grand Prix can idle rough for many reasons. The timing may be off, the fuel filter may be clogged, or it may need a tune up.
It can be stuck in 4 wheel drive or the idle control system needs attention.
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.
check your air idle control valve
valves
You might try checking you idle air control valve.
The idle is automatic. If the speed is not corect then you have to fix the problem with the idle motor.
Idle is computer controlled and is not adjustable.