190e engine hunts

Hi all;
I'm working hard on a 1987 2.6l 190e. Periodically (intermittently) the engine likes to hunt - the idle or engine speed (it doesn't care if the car
is idling or not) will jump around, as it gets worse the 02 light on the dash will flash.
This car has had A LOT of work done to try to solve this including: new igntion components (wires, plugs, etc), new fuel injectors, newish O2 sensor (it's been a little while now), newish fuel pressure reg. (also been a little while), fuel filter, etc.
Understand this only happens sometimes - which really rules out vacuum leaks, etc. (They've been checked for anyway.) Any ideas?
Thanks,
Damian
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car
sensor
My first guess would be the Over Voltage Protection relay.
Bill Balmer 1986 190E 2.3-16 first 16V in the US featured in Car & Driver - March, 1986
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