Lean combustion?

[KenS]

The manual vacuum gave interesting results with not having the periodic change in revs! Does this imply that those sudden change in revs are not caused by a lack of spark or bad injector? Or was it not quite low enough pressure to help initiate the upsets? Do you know if the right angle filter thingy feeding from the manifold to the MAP sensor pipe is OK? Wonder what would happen if it was no longer a filter and allowed transient pressure changes through to the MAP.
But ...
I have expanded one of the manifold pressure/rev pulses from '26 try fuel reg..' to see its time relation with Injector pulse width, IAC position, Air/Fuel ratio.

sml7-10-26.jpg

It shows the injector pulse width is significantly reduced prior to the manifold sudden pressure change. So I think the root cause cannot be directly related to the Manifold pressure but something that has required the ECU to reduce fueling. I guess this does bear some similarity to the original problem, so they may well be related.
ElanScan is giving ECU driving values, not necessarily values that are achieved by the IAC or fuel injectors, so its hard to know for sure what they are doing, maybe a fuel injector is occasionally overfueling causing the ECU to suddenly reduce fuel on all injectors, or maybe the IAC snaps shut occasionally, causing revs to drop, air/fuel ratio goes down causing the IAC to be immediately raise a few counts and fuel reduced. I'll have a deeper look at the O2 sensor voltages during these dips to see if there is any clue to what the injectors may be doing. (I am going away for a few days so I will probably go quite for a few days!). Good luck.