It sounds like you're jumping around checking a lot of things. Focus on one thing at a time and eliminate it.
I'd start with verifying the coil. It works hard and you probably still have the original. Usually, they work or they don't,
but sometimes they die in really strange and often intermittant ways. Good news? EASY TO REPLACE!
Here are a couple of things that may help:
( Disclaimer: I'm getting all this info from OEM Volvo wiring diagrams. I haven't had any problems like this with my '98.)
The MAF should have No Bearing on spark strength. As far as I know, it's a fuel side sensor. It helps regulate the mixture.
This is a pretty basic ignition system. The spark signal from the ECU is timing only, not strength. On or Off.
It feeds a very basic transistor circuit that you're calling a spark amplifier. The "Amplifier" is just a high speed
switch that get's triggered by the yellow/white wire from the ECU to carry the switching load.
When it gets a trigger from the ECU, it shows the coil a ground. But as far as I know, it's just On or Off.
The coil is very basic, like any coil going back for decades. It has a primary, two wire input. It's two connections are:
12v ign switch hot ( Red wire AT the coil ) , ECU triggered ground ( Blue AT the coil) to fire a spark.
For the plugs, it has a secondary, High Voltage output, the Big wire and the Ground to Chassis.
Be sure to check that ground. Resistance from the block to the coil frame should be very
If you want to eliminate that as a suspect, you can run a jumper between them.
So - Is the coil OK ? Unhook the ground side ( Blue AT the coil) and check spark at the coil by simply
shorting the ground side and releasing it to fire a spark. If it's still weak? Get a new coil.
If that doesn't get it, keep moving backwards through the system.
Spark Amp, Timing Input sensors, Dirty connectors, etc.