Hi all,

I've recently had a misfire on my car (Saab 900 2.0) that turned out to
be the coil gone bad (resistances were way out) and it's now fixed.
However, I want to understand the underlying reasons, as I can't quite
make the connections in my head.

The misfire was occasional at idle and light throttle at ~3000 rpm, and
heavy for 1/2 sec when accellerating hard from low revs.  All other
driving was perfect.

I'm trying to understand the relationship between the changes in
cylinder pressure, mixture and required ignition voltage that caused
this, but it doesn't stack up for me.  I understood that you needed the
highest firing voltage with weak mixtures at high cylinder pressures.
But the misfire occured mostly at idle (weak but low pressure).  It was
worst on hard acceleration (high pressure?, rich mixture) but fine at
high RPM full throttle (rich, high pressure).

I've seen some info about ignition voltage sag with the throttle snap
test, but no details.

Could someone explain any of this?

Cheers
Jon