02 nissan sentra keeps stalling, totally stumped

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Hopefully someone on here might be able to help me as I’m a bit stumped (and so is my mechanic at the moment)
I have a 02 Nissan Sentra GXE with a 1.8 engine. I'm having problems with my car keeps on stalling while driving on me. So far in the past three days it has happened 7 times on me. Thankfully it is only happening when it going slow (less than 10mph) and again thankfully it’s always been in good spots for a car to stall in (parking lots, etc.). Before the other day when this started I’ve never had problems like this before with the car. I think in the entire time I’ve owned my car it’s only not started maybe 3 or 4 times but would start right away if you waited about 10 minutes or so.

Now, when it stalls it is about 50/50 with not starting back up again at all, or starting right away. I am having no idea what is causing this. My mechanic thought it was the camshaft and crankshaft sensors so he replaced those yesterday since he didn't see a spark when it was dead and he was trying to start it. However even after the fix the car is still having the problems with stalling.
One interesting thing I thought was immediately after he fixed the two sensors the AC was running VERY VERY hot, as in when I had the max a/c on hotter air was coming out than when I had Max Heat on.

Does anyone have any idea what might be causing this or had a similar problem? If it helps I just had a bunch of work at the beginning of May done on the car including new drive belt, new radiator hose, brake system flush, power steering flush, fuel injection service, and a coolant flush.

Let me put it this way… Get rid of it.

http://www.consumeraffairs.com/automotive/nissan_sentra.html

so we found the problem fingers crossed it is the cars computer/ecm. <!–[if gte mso 10]>

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I do have a couple of more questions. Is it wise or have an independent shop install a new computer/ECM or should I have the dealer do it? Is it also OK to go with a used computer/ECM as long as it had warranty or should I go with a new one? Also, the mechanic told me if we get a used one that it won’t have to be reprogrammed but I’m thinking regardless it will need to be reprogrammed so that everything in the car will run correctly.

One last question is it common for car computers/ECM to slowly die or do they usually just die at once? I was wondering since this seemed to be a gradual problem not an all of a sudden one if that makes sense.

Are You The Car's Original Owner ?

Also, Have You Had A Nissan Dealer Run Your VIN (Vehicle Identification Number) To Check For "Open" Recalls And Campaigns ?

These vehicles have been subject to different electronics campaigns (manufacturer's voluntary recalls), including issues with ECM and drivability and possible stalling.

One campaign alone involves over a quarter million 02-03 Sentras, including ones with the 1.8L engine.

CSA