I'm going through this now, I changed the plugs and boot on the 6th cylinder where the misfire is. What you can do is switch the coil that you believe is bad onto another cylinder and if it brings up that the one you switched it into is bad then it's a coil.I switched mine to the 5th cylinder and it said that the 5th cylinder was bad, and the 6th was fine. So I figured out my problem, easy fix. if not it's something else such as a fuel injector, compression, etc.

 

Wife's car had the intermittent misfire again yesterday. It was damp and light rain and 50ish. She'd driven the car and run an errand closely, drove home, stopped and parked, and shortly there-after restarted and had the misfire at startup. I pulled codes this afternoon and had misfires 301 303 305 306 and a 1316.

I couldn't pull cold idle fuel trim today but pulled warm idle LT at 3.1 and 2.3
and LT trim at 2500 at -1.6 and -2.3, if that helps any. Car hadn't misfired for a couple three weeks. I may be able to pull old trims in a few hours or tomorrow morning.

 

Trims look OK. I can't see it's an air leak.

How old is the battery?

If it's not that failing I don't currently have any ideas so I hope someone else does.

 

Thanks,

A new battery was put in about 3 weeks ago. We're going to try a different gas station. I'd asked my wife not to go to a particular station and I just learned she's been going there. I think she's been getting crappy gasoline. Still, the misfire only seems to occur after the car has been run a short distance, shut off, and then restarted soon thereafter. What's the normal fuel pressure range? Initially, we thought the problem could be a leaking injector ... so that when the car is turned off some unburnt fuel causes the misfire if it hasn't had a chance to dissipate. When we changed fuel filter not too long ago ... it looked really poor.

 

A prime misfire suspect on the 3-litre V6 cars is the factory Intake Manifold Tuner Valve O-rings. They are yellow in color. Their sealing ability diminishes, causing misfires. The new-style green-colored O-rings fix the problem. You'll need two, a dealer-only item, but they are relatively cheap. Many threads here on how to D-I-Y....

 

Yes.... but this is a 4.2 NA.

So many misfires.... the nearest last thread here was a failed cat on the bank most affected, but the details were different.