Oscillating idle /hunting (850rpm 1300rpm) on all but mostly 1.9L Digijet

 

Of course there is many reasons that could happen, but on 1.9, most of the time, it's simply a bad timing, or should i say a misalign distributor with a higher idle wrongly set to compensate too much retard. The fpllowing picture show how the #1 wire on the distributor cap should be align with the botom screw (thread end side) that hold the distributor in place, BUT, this is only good if the mechanical timing of the distributor gear is right!!! If not, you now need a timing light or you can put back the gear where it should be. If yours is offset, loose the 10mm nut (red arrow and BEFORE you start the engine) and re-align WILE the engine is running, move it until the oscillation stop.... it may not stop if idle is too high, so lower the idle on the BIG flat screw on the throttle body. Now, don't be scared to play a bit with the distributor, a few deg. each side won't arm the engine, just stay around that screw tip.

A worned throttle body can also cause all skind of idle problems.
 
On 1.9L, I have also seen bad AFM (Air Flow/Mass Meter) do all kind of stuff on idle, mostly because the arm or arm surface was dammage.