[DIY52]

It looks like this was posted a while ago, but for what it’s worth I’ll offer my experienced observations about rough idle with a Chevy 3.1 V6.

There are two smooth black plastic Positive Crankcase Ventilation tubes - one going from the front valve cover PCV port to a port in the upper intake manifold just after the throttle body, and another slightly thicker one going from the rear valve cover port to a rubber port in the throttle air intake.

Try putting some Ultra Black RTV on the PCV port on the rear valve cover behind the EGR valve, and on the PCV port on the intake manifold just behind the throttle body & let it cure overnight. This will seal those ports, because the ribbed grommets quickly get brittle & flatten out or fall to pieces entirely, creating a huge vacuum leak at the metal ports where each tube goes in.

Also, check your MAF sensor wire harness by wiggling it with the engine on idle. If the engine stumbles when you wiggle the wires, you need to replace it.

The only other thing I can think of is your idle air control solenoid. I would remove it & clean the port. A new IAC valve might be in order as well.

If your engine is also knocking at idle but not when driving it, it might be time to replace the knock sensor.

I had each of these issues & fixed them. I hope this helps.