It seems the one thing people know most about VZs and VEs is that the V6’s had timing chain issues.
The issue was not the design. The issue is the motors have no tolerance to poor servicing and even factory intervals were too long, but good enough for warranty periods.
Any factory issues from the early run of the cars has been sorted some 15years ago.
So.
The O2 sensor codes. Were they pre cat or post cat sensors?
Are the O2 sensors Bosch or some other brand?
Rough idle is most commonly due to vacuum leaks and these can have more leaks than a colander.
To solve a vacuum leak, a smoke test is done on the intake system. Where ever there is a leak, smoke comes out and the leaks are found quickly.
Smoke test can be done on the exhaust to find leaks from that end.
• Brake booster
• PCV hoses where they connect to the intake plenum.
• PCV hoses where they connect to the throttle body
• PCV where it connects to the air intake pipe.
• Leaking or damaged MAF gasket
• Damaged or leaking throttle body gasket
• Damaged or leaking intake plenum gasket
• Cracked headers
• Leaking manifold gasket
• Cracked exhaust pipe in front of pre cat sensors.
Any ingress of unmetered air after the MAF sensor will throw out expected dat at the O2 sensors.
Which sensors involved matters. Pre or post.
The brand of sensors matters. Bosch will give you zero problems unless there is actually a problem and the sensor is being the goodest boy. If cheap sensors are being used, there will be months of hurt chasing non existent issues.
The purge valve could be faulty. Simple to remove and test by blowing through.
PCV blocked on the valve/rocker cover. There’s a fix for that in the how to section. Costs nothing to do.
Clean blow out the PCV hoses. Replace the hoses. Or replace the ends with new hose if you’re on a budget.
Also, clean the MAF with MAF sensor cleaner.