Just installed the replacement unit, and everything works now! Not only is it more convenient to lock and unlock the doors, I no longer have to operate the fob after the first start attempt in order to disengage the immobilizer. AND, I have a functioning alarm now. Once again, it shows how useful forums like this are. Thanks to the OP and Chuck for sharing this info.

 

Tell me more about not having to operate the fob to disengage the immobilizer. How long does it stay disengaged, Ken. Also is the alarm just the horn?

Chuck

 

When my ACU wasn't working, the only way to deactivate the immobilizer was to turn the ignition to start position (nothing would happen), then turn ignition off, then hit fob button to deactivate immobilizer, then start. Any time I turned off the ignition for more than 3 minutes I'd have to repeat that sequence to start the motor.
Now, when I unlock the doors, the immobilizer is deactivated and I have 3 minutest to start the motor without having to do the above sequence.
I'm not sure about how the alarm works. I get the flashing of the signal lights upon lock and unlock, and the door LEDs flash slowly while the car is locked. But I haven't checked the audible alarm function. The manual says it will honk the horn for 4 minutes and cause the LEDs to double flash until re-set.
After reading this part of the manual for the first time today, I was somewhat amazed at the complexity of entering the key code with the ignition switch. Scary thing is, I don't have the key code for my car, and previous owner knew nothing about it!

 

Ah, that's what mine does so I guess it's working correctly. I thought you had achieved more than 3 minutes Ken. It's really a PITA system. I only have one key so I've ordered another one from Porsche. They do it by SN. Do I think it will work when it comes in next weeK? If it does, I'll be pleasantly surprised.

Chuck