Porsche Repair: 87-924S: intermittant no spark after warmup, needle in the haystack, sensor ideas

Question
My 924S occasionally won't have a spark to the plugs (I used a timing light) after its been driven.  I've replaced the coil and plug wires. Never a problem running, and I've never had the problem in cooler weather.  I have to keep trying over and over or leave it for awhile....it turns over fine...just all of a sudden has spark again and runs fine. Is it the DME or could it be a sensor? Ideas would be much appreciated.  Thanks!

Answer
Hi Paul,

As of two days ago I wouldn't have had a clue...but yesterday I found my own no-start problem after many days of looking and testing and frustration.....

Anyway, in my case, now that I see what was wrong, it was intermittent like yours.  I found the ignition switching unit that basically is wired directly to the coil, had a loose brown ground wire at the four pronged connector.  The wire was on its bolt and its nut was there, but the the eye type connector could move...so it wasn't really grounded.  That is my needle in the haystack story.

Now... of course... my son tells me that intermittent problems are ALWAYS ground problems!  Yup!

Dave