Mystery Cause of intermittent Misfire codes 0300,0303,0305,0343

[Peter T.]

Im trying to figure out the Mystery Cause of Misfire codes 0300,0303,0305,0343.When I start my 2003 vr6 T4 these codes come on usually when I first started it in the morning intermittently. Then they went away for a while. I noticed that the POV had changed out the plugs and coils 3&5 at some point.
I had the trans and timing chain done 7000 miles ago by a very reputable shop that does T4's.
Every once in a while the same codes would come back and this spring it became much more frequent.
I replaced all the plugs with Bosch made in Germany, all coils (Bremi) and the camshaft position sensor.(Bremi)
Im still getting the codes....
It still is an intermittent issue because my local shop is having a hard time finding the root cause...
Any Thoughts??

[EuroTec]

Check fuel pressure and if you have fuel trim data see if the fuel trim is correcting towards rich. Possibly a weak or failing fuel pump.

You've eliminated the ignition as the problem.
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If it ain't broke, don't fix it!

[Peter T.]

[Abscate]

Are you sending misfires or is it a silky smooth VR6 idle like it should be?

You could have injector or wiring trouble , check for critter damage

I’m mid island near Port Jeff if you want to come by sometime
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[Peter T.]

[Abscate]

[SambaBurnsRed]

On start-up the engine runs "open loop" so combustion mix is determined by

Mass Air
Temperature >Injector volume

After it warms up the O2 sensor trim kicks-in and that will adjust fuel to actual combustion results.

Could check the mass air is in spec, and the O2 trim readings are correct.

High miles, old, leaky injectors spill fuel into the combustion chamber, also bleeds fuel pressure instead off keeping the system inflated (like a bike tire). Another possible is head gasket and coolant in there, but you'd have coolant loss over time. ECU's aren't that black and white. They report what they can, being a clue sometimes to an issue.

[Peter T.]

UPDATE!
After running it for a while the 0303 & 0305 are finally gone but 0343 still comes on intermittently at different times.....I had the timing chain done 5000 miles ago but the 0343 just started coming on 2000 miles ago.....

[Peter T.]

Latest Update: After replacing all plugs and coils and Cam position sensor (all OEM German) All codes are gone but the 0343 code became 0341. I took it to a German car shop that is very knowledgeable in Eurovans (owner drives one daily) and he determined that its the cam timing actuators. He didn't have time to dig into so I got it home (drove great even though the code kept popping on) I flushed the motor with Liquid Molly and now code doesn't come on until I start it. It will drive without the code coming on, only when I start it.......any thoughts?......gummed up actuators?

[SambaBurnsRed]

How is your battery, battery connections and grounds? You might try a lithium booster on starting, as a test.

Marginal devices do strange things on low voltage (like starting). My Range Rover threw misfire codes below -2 DegC. I went to a Lithium battery (AntiGravity), which corrected the problem. Lithium power is amazing. Range Rovers devour current & batteries (short life) so the LiON provides solid power and voltage

[Peter T.]