Glad to get your reply. It confirms what I found.
I suspected the culprit might be the fan module after reading others' experience, so I dis-assembled it. It had no identifying marks on it, but I found that the circuit board components had date codes from 2007, so I knew it wasn't original equipment.
I discovered that the large 220 uF 35 volt capacitor (C3) in the middle of the board was slightly bloated on the top, indicating it was likely failing. Using an ESR meter, I found it had very high equivalent series resistance (16 ohms), and replaced it. But I installed a larger 470 uF 35 volt cap instead, believing that in a power supply filter more capacitance is usually better.
Before the repair, the wiper would jump slightly nearly every time I started the car. Since putting the repaired module back in service two days ago, I haven't had one instance of wiper or washer action.
Now, I don't know whether going to a larger value capacitor had any positive effect. It may be that the 220 uF capacitor works just fine as long as it's good.
I took a few photos after repairing the board, while re-assembling the module.
Here's one. It shows the new (light blue) cap installed and the bad one next to the board.
FYI. When re-assembling the module, don't over-tighten the screws on the heat-sinks of the two power transistors. You might squash the soft insulators underneath them, and short out the circuit.
Tuesday, May 24th, 2011 AT 3:28 PM