Threads like this make people want to start learning how to work on their own cars. I could throw my vote in there, but y'know internet diagnostics aren't easy. That's why 1TurboFocus wants a datalog before he puts his .02 in. Without some sort of diagnostic- we're just guessing.
The symptoms can be caused by a number of conditions- many have been covered so far. Since you've tried so many things, I have to be careful not to double track. Also, I think your problems must be caused by either a combination of problems or an uncommon problem.
1) The collapsed PCV vacuum line can cause low idle, which could be the stalling part, but not all of your problem.
2) EGR issues including the DPFE failure. The DPFE is what controls the EGR, it measures exhaust gas pressures, and tells the EGR when to open or shut. Usually, odd readings of this device will trigger DTCs (diagnostic trouble code) of some sort. Sometimes the DPFE fails without a code, and I could see where the EGR could be stuck closed and the DPFE not know it. That being said, your symptoms seem to be more extreme than a stuck closed EGR will cause, and symptoms of a closed EGR will go away as the engine warms up. This could be part of the problem if multiple problems are causing this issue. I would remove the EGR, clean, and check to be sure it has it's range of movement. To test, simply put a small hose on the vacuum port, turn the EGR around so you can see the valve, and suck lightly on the hose. About enough breath to fill one cheek is enough to operate the valve. If it seems like you're sucking forever- there's a hole, and the EGR is bad. Other than that just watch to see that the valve opens and closes completely.
3) I don't think the car is really backfiring. Backfiring is nearly non-exisent in computer controlled EFI vehicles that don't have some sort of valve timing failure- which you don't have. Backfiring shoots fire up through the intake, and usually happens after a vehicle has nearly stalled out or stalled out. I think what you're experiencing is fuel popping or firing in the exhaust. This can come from any sort of problem that allows either too much fuel or incomplete combustion- which would allow unburnt fuel to enter the exhaust. If you thought the other list was long, this one is longer. From incorrect spark plug gap, plugs in the wrong heat range, and on to clogged catalytic converters- we've got lots of causes for unburnt fuel. I'd expect a DTC from the upstream O2 sensor, and so I wonder why that one isn't doing it's job. Although the symptoms fit, ehh, I'm a bit reluctant due to lack of DTCs. I really wish you would've gotten the actual number for the DTCs that the car's computer is throwing. That would aid with our internet diagnostic.
4) I'd like to know when this started happening. I assume you didn't buy a car with these sorts of problems. That might help with some diagnostics. I was thinking you might have a throttle plate that is not set properly, but someone would've had to do that at some point. You haven't had any boyfriends who tried to adjust your idle screw have you? (don't do it, there is no idle screw)
That's my first stab at it. I'm late for work now. Maybe later.
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