So, a few weeks ago, the car started getting a problem where after accelerating to a certain rev range, (sometimes 3k, 4k etcetera), and then hesitates/refuses to accelerate further. Flooring it at this point seems to produce weird popping noises (maybe misfires?) and after a while, the rev range seems to keep going down up to the point where (in one instance) it stalls. At this point I noticed that (coincidentally), the fuel pump was making very loud whining noises. I replaced the fuel pump, the car felt better for about an hour, and then started to make the same problem. The only code that popped up was the one indicating catalytic converter efficiency (it's currently on a test pipe so I assume that's expected).

While waiting for the service appointment, I drove it another time, and this time it stalled to a stop and I couldn't start it up - had to tow it home. At this point, it started producing P0131 (O2 Sensor Circuit Low Voltage Bank 1).

Now, starting it up is resulting in it stalling immediately, see video for further detail:
Anyone has any clue what this could be? I'm purchasing an O2 sensor to replace it... but is this really the cause?

 

Have you had any recent engine work done? Replacing parts? Modifications?

 

I've just replaced the IACV (with a new OEM model) a few weeks ago because it was bumping revs up and down on idle.

 

So, these symptoms are occurring, after bypassing the catalytic converter?

 

I bought the car a little over two months ago. After two inspections (body shop and mechanic) and a drive, I had never seen these symptoms. The cat was already bypassed when I bought it.

They started happening after I drove it for about 200km.

 

Bad fuel, perhaps?

 

It’s a longshot, but there is a chance your catalytic converter may be plugged. I wouldn’t dig in too much until you deal with the o2 code, as a bad cat is unlikely. If a cat get too hot from bad gas the honeycomb can shrink and ball up. I had it happen years ago and the symptoms were just like yours. Basically the honeycomb balled up and came loose, then once got it would literally get pushed into the exhaust pipe and choke the car. That being said, it’s likely an o2 sensor.

 

Since it has a test pipe installed I don't think the cat would cause any problems.
On cold start the car should be able to idle for maybe a minute of more before the ecu cares about the O2 readings.
So that code is most probably a secondary problem.
Get someone to spray starting fluid, brake clean or similar in the intake and see if it still idles, then you will know there is still a fuel delivery problem.

 

x2 on flanders, the thing that may have killed the fuel pump may be in the fuel system (lines or injectors). may be the fuel itself or contaminants.

also protip: do not assume the fuel pump is working, verify everything and redo if need be.

 

Small update:
Mechanic opened the car today and we found an absolute mess under the head. One of the camshafts was rusted at some point and some genius tried shaving it off - but alas that's not the problem.


The main large head cover gasket was broken, and the donut ring gaskets were completely missing. All tension leads were soaked in oil. We're still investigating. Mechanic is convinced that this at least could have caused the issue. The remarks you guys made about something malignant remaining in the fuel lines is still very probably... I will raise it and we'll see if we can bleed and clean them. If it's any consolation, the old fuel pump died because it seemingly was the original fuel pump and must have worn down (100k miles).