94 Grand Am Running Rough

I just bought my son a 94 Grand Am 4-door with the 2.4L 4 cylinder for $800. Car is in awesome shape, has high miles, but motor was replaced and has about 70,000 on it. Car has an extremely annoying sputter at idle and under entire RPM range, but is less noticeable at higher speeds. Guy we bought it from says its a fuel injector that needs to be replaced, but I am sceptacle. Does anyone know where to start or is this a typical symptom of a bad fuel injector. Runs fine otherwise other than the ABS and BRAKE lights being on.

It could be:

A. Bad injector or dirty fuel filter.

B. Bad spark plug or coil pack.

C. Bad head gasket.

D. Bad head.

Hope its not the last 2 as they are rather expensive to replace, and if its something you are doing yourself it will take 10-12 hours depending on how skilled the person doing the work is.

look over all your vaccum lines and make sure no leaks are present

Checked vacuum lines all seem to be ok. I am thinking it is probably a fuel injector or the coil. How do I tell which one it is? And if it is a fuel injector, how will I know which one to replace or clean for that matter.

Unplug the electrical connector to the fuel injectors one at a time, start the car if it runs the same thats the cylinder with the problem. To test the coil pack you need a multi tester to measure the reisitance, I dont' remember the sequence someone on here should.... If the coil packs check out ok test the ignition control module its the little black box under the coil housing.

i would saying using the straw technique would be better to find out if each injector is working