ffwd

Thanks for all the feedback. I think I will take this up with the dealer, because my wipers are definitely not behaving nicely

@ Spoddle: In my car, when I "disable" the auto wipers by leaving the stalk in position 1 when starting the car, that just leaves the wipers totally "off", not in a timed intermittent mode. That would be great if it did.

@ DLennox: Unfortunately, my car does not have the package with those additional PCM functions.

@ Minok: I get your point about "not based on speed directly". Somewhere online I had read that the wiper control algorithm is speed-dependent , and if I remember correctly I even saw the actual control equation/function in which one of the variables was the vehicle speed. Also, on this forum I had read a post by super moderator "ltc" dated 10/28/05 about the rain sensing wipers on the Cayenne, which copied text from Porsche factory technician documentation about how the wiper function is speed dependent with respect to speed thresholds at 2.5 and 5 mph. I don't know if the C4 wipers work the same as the Cayenne wipers, but this is more info for consideration.

Thanks again.

Spoddle

Interesting, I meant to test it myself today since it rained. I wonder if after starting you adjust the sensitivity if it will then stay at a set interval. I'll test it tomorrow if it rains again and report back.

ffwd

Referring to my OP: problem solved.
It seems the erratic operation of my 997.2 rain sensor wipers was caused by the cord of my V1 being coiled/wrapped around the little tube (wiring channel) that goes from the rain sensor up to the headliner. I had done that to keep the hardwired cord tidy as it runs to the V1 directly to the right of the mirror mount. As a check, I changed how I run the cord to the V1, without coiling it around the rain sensor's wiring channel, and lo and behold, now the rain sensor wipers work excellently. The V1 cord loops must have caused interference or added enough inductance to the circuit of the rain sensor to screw up the rain sensor signals. Weird, eh?

Minok

I could imagine the rain sensor being a very low voltage signal. If you wrap the power cable around it, then that power cable probably has all sorts of ignition and other power-consumer noise on it.. and wrapped around it, its like a coil inductor, and transmits the electromagnetic signals to the rain sensor wire bundle. I doubt the rain sensor bundle was heavily shielded, as it wasn't intended to be wrapped inside a power cable.

Glad you found out what was the cause, and it serves as a reminder to us all that you cannot just use existing wiring as structural support without considering the electrical effects as well.

Edgy01

As an alternative you can simply avoid using RainEx at the sensor location.