rough idleing

My 1996 monte carlo has 3.1 it idles rough at stop lights or anywhere your stopped. But works fine when being driven. Any idea what could be causing this? Can not put on scanner as wires are of connection where scanner plugs in to.

i saw that no one has replied to this yet, and i don't know much about cars, but when my monte carlo was doing that, it also started stalling randomly. it was the mass airflow sensor. i don't know what else your car is doing, but that's what was wrong with mine.

Try checking the Idle Air Control motor

Before replacing the MAF I would replace the PCV and see if it helps. A clue to look for is if the PCV chamber is coated with oil on the outside. A leaking PCV can cause a rough idle because it can not create a vacume seal. It is also way less expensive than a MAF. If you decide to replace the PCV buy the entire kit, it will cost about $24.00. The valve itself only cost $6.00.