Volkswagen: 1989 VW Cabriolet engine oil light flicker/sporadic engine shutdown, light flicker, air control valve

Question
Hi John,

I have a 1989 cabby with the 1.8L engine that intermittently/sporadically shuts down after oil led flickers at idle, or, under stop and go slow driving conditions only.  The oil gauge on console generally indicates a minimum of 1 bar (fully warmed up engine) which, to me is approx. 20 psi.  I installed a new pressure sender(0-5 bar) after hooking up a direct reading gauge to the sending unit port at head. That direct gauge agreed with the new sending unit/console gauge readings, so i trust the new readings i'm getting and suspect electrical problems as opposed to mechanical problems.  No unusual valvetrain noise or knocking, no leaks of any concern, i'm running 10w-40 penzoil. since I've owned it, i've put over 1000 miles on it, and it only drops off during hot conditions. engine runs fine otherwise, however, idle tends to drop off whenever the flickering oil lite and shutdown shows up.  Can you please give me some of your expertise and advice?  thanx in advance,  Tracy

Answer
The reason the oil light flickers is due to the alternator voltage dropping as the car cuts out. the possible reason for this is air leaks in the intake system, or even possibly the idle air control valve sticking or malfunctioning. also the throttle valve may need cleaning out, or the co may need adjusting.