Well my service engine soon light popped on now my blazer is running real rough spitting and sputtering seems to drive ok but at an Idle its not so good

There are several potential issues that could be causing your 2005 Chevy Monte Carlo to spit and sputter while driving. Here are a few possibilities:

1. Fuel delivery issues: If your engine is not receiving the correct amount of fuel or air, it can cause hesitation or rough idling. This could be due to a clogged fuel filter, a malfunctioning fuel pump, or a problem with the air intake system.
2. Ignition system issues: A faulty spark plug, ignition coil, or other component of the ignition system can cause misfires, which can make the engine hesitate or sputter.
3. Emissions system issues: Your vehicle's emissions system is designed to reduce harmful pollutants in the exhaust. A malfunctioning component of this system, such as the oxygen sensor, can cause the engine to run poorly.
4. Electrical issues: A damaged or worn electrical component, such as a sensor or relay, can cause the engine to run rough or stall.
5. Transmission issues: If your vehicle is experiencing transmission problems, such as slipping or shifting issues, it can cause the engine to hesitate or sputter.

To determine the exact cause of the problem, it's best to have your vehicle diagnosed by a certified mechanic. They can perform a diagnostic scan to check for any error codes or issues with the engine, transmission, or emissions system.

Check the fuel pump , filter, throttle position sensor.

Is the check engine light on ?
Have you checked the fuel pressure yet ?

If the check engine light is not on I would look for a stuck EGR valve. It's located in the front of the engine towards the middle. Take it off and look for carbon deposit holding pindle valve open. Also you may have a blocked up catalytic converter. You may have to take that off and see how the car runs. If the check engine light is on look for codes first by scanning it or having it scanned. They usually do this for free at Autozone. Hope this helps.

ing. mod. and coil pack may be starting to go bad had same trouble with mine only a tune-up problem solved then came back be fore i put car on di machine found that coil pack was bad! when if you scange coil pack or ing. mod. replace all, if not will have problems again.

How about a coil pack? Is there a service engine soon light lit when this occurs indicating a hard code stored in the computer?

change the egr valve

Sounds like a vacuum leak, i would check that first

Engine light could be from the spitting and sputtering, sounds to me like maybe bad spark plug wires, possible an ecm issue, what kinda code is it giving you when the engine light comes on?

check your spark plug wires.