I have a weird problem. So I have a 2004 Cavalier 2.2L Ecotec, and it intermittently stalls on me, or will not fully start right away. It's an automatic, and when it stalls it's usually in reverse or drive. When it doesn't want to start, it does crank, but kind of sputter/hums for a brief second and stops.

A little background on what I've tried and replaced:
A year and a half ago the fuel pump went out, so I had to replace that. At the time I did not replace the fuel filter (I know, bonehead move).

Last summer it started stalling again. I took it to a friend who verified that it was getting fuel, so that it must be something spark related. Side note: he didn't measure how much pressure it was actually getting off the fuel rail. He deduced that it was probably the ignition control module which sits on top of the coil pack cover. Replaced that and went on my merry way, or so I thought. About a month later it was randomly stalling / failing to start. I could eventually get it to start enough to drive it around for a while, but it progressively got worse.

Fast forward 6 months or so and now it's happening regularly. It stalls while I'm driving. Sometimes it'll work just enough to get me some place far away, and then it wont start back up for a while leaving me stranded. At this point I have another friend look at it, and he deduces that it's the coil packs. We went off to the junkyard to buy a whole new coil pack cover unit and swapped out my old one. No dice. He suggested that we take it to the dealer and pay for the diagnostic, and he would help me fix whatever the dealer said was wrong.

We get it to the dealer, and they say that it was the coil packs that were failing. Ok, so maybe the junkyard wasn't a very good deal. Off to the autopart store we go to buy a replacement. We put a brand new coil pack cover on and it starts.. but not for long. It's soon back to it's old tricks again. I try leaving the battery unplugged over night thinking it may need to reset the computer or some other witchcraft, and it seems like it worked, for a little while.

Back to the dealer and they're now saying it's the PCM ECU, and are quoting way too much saying it needs to be installed by the dealer. I find a guy online that sells refurbs with a year guarantee, and he has the GM TECH II tool to program them. Get it all set up for my car, and reset the passlock and the car seems to be working for a bit. Take it out for a spin around the neighborhood and it fails. I'm close to blowing it up at this point.

So I get to thinking, you know I never replaced the fuel filter, I wonder if it's restricting the fuel flow just enough that it's making it stall at weird times.. I go pick up a new filter and replace the old one. I noticed some dark color fuel come out of the filter and thought that could not be good. Once the new filter was on the car was revving like it used to, and it seemed to not hesitate as much! It's interesting how you get used to something running like crap and don't notice a difference until you replace a part. Anyways I thought I finally had it beat. I was driving around, felt like I conquered my little POS, then I get it up to the driveway and it stalls. DAMN! It doesn't start back up for a while, so I let it cool off, let the fuel pump prime, wait a couple minutes and it starts, but then soon stalls in reverse.

At this point I don't know where to go. I've had two friends and a GM mechanic look at it and tell me what was wrong, but when we try to fix those problems the symptoms do not go away. Any ideas?

Looks like it was the CKP sensor.

So what ended up being the problem? Did you get it fixed?