Car loses power after warming up; 02 sensor didn't help, now what?

[KevRC4130]

My 325i starts right up and drives great for 10-15 minutes. It has full power, can be redlined, idles smoothly (for what it is), and all in all seems perfectly healthy. In fact, it almost seems like "italian tune-up"-style driving helps the engine run how it should. However, after that 15 or so minutes is up, the power is lost, and it ultimately gets to a point where it cannot even rev past about 1000 rpm and simply stalls.

I replaced the 02 sensor today. That definately made the car idle smoother (it's always had a somewhat oscillating idle, which seems to be fixed). Otherwise, though, the problem is exactly the same.

Another strange thing is that the car did this for about a week this summer. For some reason, it stopped doing it, and I've made it this long without changing a thing. However, about a week ago, it started doing it again, and it wasn't going away this time. I was expecting an oxygen sensor change to do the trick, but it hasn't.

Any ideas?

Thanks!
Any ideas?

[nando]

coolant temp sensor

[KenC]

O2 sensor shouldn't have had much of an effect. Def check temp sensor as stated above.

[kronus]

Your AFM may be suspect. Check that the flap is not binding, the plug connection is solid, and the resistance is within spec.

[lordofthewaters]

+1

Could be a failing fp as well.

[jlevie]

For that set of symptoms, my first suspicion would be the fuel pump or relay.

[nando]

if the fuel pump were bad, it would run poorly when cold too - since cold running can use up to twice as much fuel as warmed up/closed loop. a relay would lead to a no start issue or the car would just shut off.

check the coolant sensor..

[jlevie]

Not necessarily. The pump or relay may work fine when cold, but misbehave after it heats up. A fuel pressure check when cold and after being driven will quickly tell if the fuel system is the cause of this.