Strange fuel trim readings: zero short-term but high long-term

[OldHoopsJunkie]

I have a 2004 Audi S4 (V8, 4.2l) with 94k miles. It is suddenly having major misfire issues with the check engine light blinking. Drove it 2 miles home that way.

Started engine today to read codes only. The only error codes are P0300 and four associated misfire codes for all the bank 1 pistons. The problem since yesterday is too new, I believe, to have generated a new error code by now. I suspect that it is one or more coils gone bad. Spark plugs are relatively new.

I am getting two very puzzling readings: Short-term fuel trim on both banks is flatlining. Both read zero over time with no ups and downs at all. They weren't doing that a week ago.

At the same time, long-term fuel trim on bank 1 is over 12, very lean. Long-term fuel trim on bank 2 is about 6.4, also too lean.

FIRST QUESTION: Why would the system show zero short-term codes on both banks when the long-term codes seem to be reading clearly and showing lean-mixture problems?

The history includes having replaced PCV valve with a new, aftermarket valve, which now buzzes loudly and constantly while engine runs. The buzzing strangely stops when I press it in (forward) toward the cylinder head. It is creating suction in the crankcase (tested at the oil cap), so it is working. I've ordered a new OEM PCV valve.

EGR valves: Bank 2 valve was in excellent condition in September. Could not get bank 1 EGR valve off to check it; the last bolt seems to require either a special tool, an extremely disfigured and undernourished hand, or removing the engine to get at it.

I have also cleaned MAF sensor twice; I'm told (local technician) that the cleaner can damage it if sprayed on more than the wire, which I did. I've ordered a new one, which is on its way.

QUESTION 2: I have these suspects below for the Bank 1 misfire codes. Are there other possibilities?
1. Leaking fuel injectors that side. I pulled them out but cleaned only one and replaced the o-rings and pintels on only that one. Dumb.
2. vacuum leak affecting that side only. Can't find one, and the lean reading suggests possible vacuum leak affecting both sides, so codes on one side are a mystery.
3. Camshaft tensioner or plastic bracket (based on an Audi posting elsewhere)
4. Something electrical that side.
5. EGR valve on that side, the one I couldn't get off.
6. All four bank 1 coils misfiring a little until one blew entirely.

Thank you for any reasonably diplomatic responses.

[VinnysS4]

Have you scanned the car with a vagcom? If the misfires are only on one bank of the engine, that helps narrow it down a little. Start by swapping coils from one side to the other. Might inspect the plugs while you're in there and complete a compression test while you're at it. Do the misfires follow the coils? OK. Try swapping O2 sensors from one side to the other. Do you have any raw fuel smells near the fuel rails? A leaking fuel line sucking air could cause the engine to misfire too. Basically try anything you can without just throwing parts at it. I've read that a bad coolant temperature sensor can cause this as well. Not sure if it would make only one side misfire, but you never know. Scan with vcds and post the results