What sort of mileage?
Is the car idling perfectly or does the car shake briefly but periodically enough?
In my experience the Lagunas
seem to fail silently for a spell, causing sporadic misfires until the problem is serious enough to register as problematic misfire via the toxic fume light.
itself is also the cause of such issues when the plates actuators "stick" but the injector duration is changed in response to acceleration.
Of course it could be many sensors, including the crankshaft position sensor where specific revs are involved. It could also be the O2 sensors becomming "slow" whereby the
adjusts fuel richness incorrectly in that feedback loop.
I would try everything starting from cheapest..
Filter + Air Filter + Spark Plugs.
to swap in place of the existing 4 in turn to see if any are causing the problem.