Intermittent Multiple Cylinder Misfire

[fallingreason]

So, my car has been running a little wonky, underpowered, not making as much boost as it used to. Just changed the oil and plugs, no change.

Car used to boost 14.5 with stage 1 unitronic, now boosts 13, maybe 14 sometimes depending on engine load and air temp.

Cleared very old codes for some misfires and Boost Regulation, reset Throttle Body adaptation. Overall the car is driving better after VAG-com clearing and readaptation, more responsive and crisper throttle, but boost and power is about the same.
The next morning I had three episodes of blinking CEL misfires on a freeway commute where I couldn't pull over. These happened at minimal or no boost, just steady cruising. One of them had very noticeable sputtering for about a minute. Then the car drove fine for 2 days. Third day after a pull, but not WOT, the car would not idle right and vacuum was jumping around from -12 to -8. Shut off, restarted engine and same idle issue. Drove to next stop light and it was fine.

Pulled codes again, Multiple Intermittent Misfires, all cylinders as well as codes for misfire on Cyl 1-3.

What's going on??

Would a boost/vacuum leak be this intermittent and allow the car to run fine and do WOT pulls between these couple of episodes? I get -20 to -22 vacuum unless AC is on or an accessory is used like power steering. If I hold RPMs at 2k at idle vacuum drops right back to -22.

Things that have been replaced in the last 20-30k... MAF, DV (710N), Fuel Filter, Coilpacks (Hitachi), has new copper plugs gapped to 0.28, air filters, Breather hoses & PRV, pancake valve, a few check valves (not all).

I'm thinking it may be the CAT which could also explain the decline in boost? Can a backed up cat cause misfires at times?

I'm kind of stuck after searching. Dont think its coilpacks with all cylinders misfiring. Could a wastegate/turbo issue cause this? I would think that would be more consistent.

I would also think symptoms would be more consistent if it were a harness problem.

Any ideas? Blocks I should log?

Thanks!

[Luis_Heineken]

did you replace the coils & plugs?

[AutoMax]

Coil wiring?

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[fallingreason]

Harness looks fine.

Plugs are fresh. Doubt it is coilpacks unless all 4 went at once.

[AutoMax]

Well, If plugs are new and coil packs are good. Then I would assume wiring or ecm if its misfiring. However you can also have misfires due to fuel/boost leaks. I would take some logs. How do the injector harnesses look? Have you done a boost leak test?

In regards to logs. You want as much as possible really. Boost/actual vs requested. Rpm. Intake temp. Misfires. Knock. Timing. Maf. N75. Afr.


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