Good evening all. I was wondering if you could help me diagnose a problem with an 09 Pontiac Vibe, 1.8L Engine, with 160k miles. I started the car two days ago and it stalled in the driveway. It was low on gas, but not out. So, I went and got gas. Seemed to run fine from then till about 3pm. Then I noticed a persistent dip in the idle. Going from 1k to 500 (nearly stalling) then back up again. No check engine light. It was due for an oil change so I went and had it done. On my way it stalled at a red light, restarted with some trouble, and then made it to the lube center only to stall again in their driveway. Didn't want to restart for the mechanic driving it in, they had to give it a bit of gas to crank and go into the bay. He suggested it was the idle air sensor or valve, because of the fluctuating RPMs. After the oil change, it stayed idling during my paying, signing and getting back to it. Seeming to be no more trouble. I pull out of the lube center and the check engine light comes on, as well as the VSC off light. I went to autozone, Code read misfire in cylinder 4. I replaced the spark plug, and the ignition coil. We cleared the code, nothing changed. Still no check engine light. Still the fluctuating RPMs, now to the point where if you stop it stalled. I made it home (technically running every stop sign between autozone and here) and it died in the driveway. Now it will not restart. It tries to crank, but will not start. I did all four of the spark plugs today, Coils were just bought a few months ago. I sprayed starting fluid in the intake and got an attempt to start, but no full turn over mostly just the constant vrr vrr vrr vrr of an attempt to start. I'm thinking fuel or air problem. But I have no idea how to diagnose it before just throwing parts at it. Can you help? Thank you for your time!