Well, I went out in the 5^ weather and ripped apart the dash tonight. Interesting enough I found that the remote start was spliced into the Theft Exciter Module wire going into the theft control module. What that means is that all activity, weather remote start OR normal key operation, is routed thru the aftermarket remote start. So... tomorrow, after my fingers and toes thaw out, I am going to pull the remote start wires off the anti theft module, and reconnect them the way GM meant for them to be. If I can get this to consistantly work, I would have then found the aftermarket remote start to be the issue.

Of coarse I spent quite a while today troubleshooting this. I have yet to find a cause. In fact, it has been working flawlessly ever since I tor into the dash. The only thing that has changed is that it is about 30^ warmer out now than when the car had the starting issues. So for now, my wife will drive my C3, I will drive the Aurora, and I will keep my aunts car at my house for a week or so as a backup. I can only hope that eitehr it fails again and I can fix it for good, or the problenem never comes back again (not as likely).

After it working all weekend, this morning when I want to go to work it finally does it again. Anyways, I did come across a new scenario. I got the key to work in the ignition, but the remote start would not crank. I got it working again pretty quickly by unplugging and replugging in the connection to the theft module in the dash (driving with no dash trim on). So I am driving the car today hoping that it will keep failing and I can keep fixing it. I think my next step is to unsplice the remote startout of the exciter modules wire feed and put it back to a stock connection. Although the remote start won't work at all in this scenario, i'd be really interested to see if the key starts to work consistantly.

Ok, I have some new info again. I have found the last two days that the remote start system, including all functions on the aftermarket key fob, are not functioning correctly. This means that when I go to unlock the doors with that fob, the lights flash, but the doors don't unlock. Same goes for locking and starting. This is an occasional thing, but happens fairly frequently now. But when that does happen now, the key continues to work correctly. Maybe someone can verify this for me, but it seems that the aftermarket remote systes/entry system is faulty.

I would have to agree with you that the aftermarket unit is faulty. I once had an aftermarket unit that was acting weird and I just tore it out, replaced it and all was back to normal.

Especially since the fob isn't working properly etc...

Could you just unplug the remote start brain from the wiring harness and use the car normally? I know you won't have the remote fob use anymore but that might be a quick way to determine if the remote start is causing issues. That way you don't have to actually rip it out. The wires would still be tapped into the modules and whatnot but shouldn't affect anything unless they have the remote start inline with the cars' components so unplugging the remote start would break the connections.