The door locks of a 1987 or 1986 (the later models are slightly different) sometimes don't close or open properly where the open-close  cycle does not stop but repeats itself. Sometimes this is also called "the crazy door lock phenomena".

The explanation is rather simple:

The door lock actuators are little 12v motors with a gearbox and a contact switch.  The locks of both doors need to work simultaneously, since the is a central locking feature. If one door locks, it triggers the other door to also lock. So both lock devices must be in sync. Open... or closed state. But what happens when they are not in sync?

One door lock closes, says to the other lock: hey.... you must also close. the other lock starts to close but fails to make the "hey I am closed" contact in time, causing a signal to the other lock saying "hey I'm open, you must also open." This makes the locks cycle, and if you're lucky it cycles just once and stops there. Sometimes they keep cycling.

The problem may be caused in the bad switch (sliding contacts over a copper strip) in the gearbox. Opening and cleaning them may help. The motor assembly must always and every time make one normal turn and then stop. Another thing is adjusting its position (move the assembly slightly) which changes the mechanical load on the gearbox slowing it down or speeding up.

The door locks are cross wired. If one will not lock because the door is open then the other resets to the unlock position. The same occurs if one of the locks is not adjusted properly.

The electric door locks look like an add on. I guess Porsche planned on going with the vacuum locks until customers complained. Instead of modifying the fuse panel for the door locks Porsche added two separate fuses in fuse holders and attached them to clips at the top of the panel. Sometimes you have to go searching for the fuses because they fall down behind the panel. If one fuse is blown the door locks will never cycle right. They can even get into a never ending loop of opening and closing

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fixed.

4 items need to be loosened. The two Hex head bolts ....and the 2, 8 mm bolts/nuts (one of which is hidden out of view but you are able to get a wrench behind it.) Once these items are loosened you can slide/adjust the whole assembly fore/aft.
I closed my door, let the locks go through there spastic cycling and as they did i slid the assembly slightly. Didn't take much but the cycling stopped. Snugged the bolts and done. Not going to put the panel on or leave my keys in the car just yet.....going for a few days of door closing here and there to see if it is truly "adjusted" as several time the locks would cycle when the passenger door was closed. The jarring/impact
was apparently enough to effect the adjustment. As mechanical and crude as it looks behind there, it is VERY sensitive to adjustments.

Tony.