Issue happens at all RPM's, and starts up within a few seconds of starting the car. Engine RPM's go up and down maybe 200 RPM each time, and drop low enough at idle that the engine threatens to die. If I leave it long enough, the engine will die like I turned the key. This is the weird part - the RPM's don't slowly drop. It;'s not a surging idle that goes up and down, like you tapped the gas pedal and let the RPM's drop down. The RPM's drop almost instantly like the whole engine has lost electrical power. Less than a second later, the engine recovers and the RPM's jump back up almost instantly. Engine revs like normal, but higher RPM's don't seem to affect the issue. The engine doesn't sound like a miss on a cylinder or two, it sounds like the whole engine is cutting out. I can record a video on my phone if the description isn't clear.
I first thought it was a fuel problem, so I replaced the fuel filter. No change, though it was at least 10 years old so it needed to be done.
Next, I put a fuel pressure gauge on the schrader valve on the fuel rail, then started the engine. I had a constant 38 psi as the RPM's bounced up and down. I pulled the vacuum hose off the fuel pressure regulator, just to see if anything changed. The fuel pressure went up a couple of psi, but was solid until the engine died. Fuel pressure regulator was replaced in 2019, but the steady fuel pressure tells me it's not a fuel problem.
I don't know electrical very well, but I did put a voltmeter across the battery. It was 11.88v with the engine off, and fluctuated between 14.38v and 14.44v while the engine ran. I couldn't tell if the tiny fluctuations happened when the RPM's jumped, but as far as I know anything over 14v is fine.
As I said, I don't really know engine electrical or how to test it. My first guess would be to check if engine electrical was fluctuating with the RPM's, but again not sure how to test it. I'm very willing to try and learn, I'm just not sure what to do.
I first thought it was a fuel problem, so I replaced the fuel filter. No change, though it was at least 10 years old so it needed to be done.
Next, I put a fuel pressure gauge on the schrader valve on the fuel rail, then started the engine. I had a constant 38 psi as the RPM's bounced up and down. I pulled the vacuum hose off the fuel pressure regulator, just to see if anything changed. The fuel pressure went up a couple of psi, but was solid until the engine died. Fuel pressure regulator was replaced in 2019, but the steady fuel pressure tells me it's not a fuel problem.
I don't know electrical very well, but I did put a voltmeter across the battery. It was 11.88v with the engine off, and fluctuated between 14.38v and 14.44v while the engine ran. I couldn't tell if the tiny fluctuations happened when the RPM's jumped, but as far as I know anything over 14v is fine.
As I said, I don't really know engine electrical or how to test it. My first guess would be to check if engine electrical was fluctuating with the RPM's, but again not sure how to test it. I'm very willing to try and learn, I'm just not sure what to do.