[Wyloch]

Only when hot (~10 minutes), I get sporadic bursts of engine fluttering...it almost feels like a misfire. And it only happens at low revs, during acceleration.

But it hasn't thrown a single codes, and this has gone on for months.

Here's what I have done, to no effect (the symptom is totally unchanged):

- Replaced all six sparks
- Replaced all six coils
- Replaced both VANOS solenoids
- Replaced both camshaft speed sensors
- Performed oil and fuel cleanings, followed by oil change
- New battery (voltages all check out fine with meter anyways)
- New engine air filter

I have one final guess at what it could be. But instead of saying it, I'm hoping to get a truly independent opinion here...

Thanks for any insights.

Edit: Oh, it's a 2009 328i bone stock base model

[Gemini562]

I'd consider looking into fuel delivery issues or a clogged catalytic converter, which might not always trigger a fault code but can impact performance under specific conditions like heat and low RPM acceleration

[gbalthrop]

Originally Posted by Wyloch

... it only happens at low revs, during acceleration. [Please be more specific re Load, RPM, Throttle position]
But it hasn't thrown a single codes, and this has gone on for months...- Replaced all...I have one final guess at what it could be...

Welcome to the Forum! Nearly 10 years: TWO posts?!
I'm NOT trying to give YOU a hard time. However, Throwing Part$ rather than Diagnosing is endemic on the BMW Forums.

QUESTIONS:
1) Which engine? N51 or N52? Last-7 Characters of VIN?
2) What Make/Model Scan Tool or Diagnostic Software (INPA/ISTA) do you have available?
3) What Modules can that Tool connect to? DME? EKPS?
4) NO Warning Lights on Instrument Cluster when "Fluttering" occurs?
5) Can your Scan Tool display "Live Data" or inputs to DME from Sensors while engine runs?
6) Can your Scan Tool connect to EKPS (Fuel Pump Module)? Can it "Activate" the fuel pump, and/or display Pump RPM, or % of max speed, showing BOTH the "Target Speed" and "Actual/ Current Speed"?
7) If YOU do NOT have a Scan Tool capable of reading "Hexadecimal Codes" (Hex-codes) in BOTH the DME & EKPS, go to nearest large Parts Chain, such as Advance Auto, AutoZone, etc. and get codes read FREE. If there are any fault codes in EKPS Module or DME Module ask to have "Freeze Frame Data" for any such code displayed, and take photo/ copy any FF Data Screen. Freeze Frame Data is a "Snapshot" of system conditions (Pump Speed, voltage, etc.) at moment Fault Code saved.

"Misfire" is a slowing of crankshaft rotational speed, as measured by Crank Sensor Signal to DME, due to reduced Power Stroke on one or more cylinders, as compared to other cylinders in firing order. So if you have a condition, such as low fuel pressure, that affects ALL cylinders equally, you will have NO "Misfire" code set, as you do NOT have any "misfire" by that definition. The engine MAY sputter or hesitate, but NO DME Code unless there is a sufficiently-long LEAN condition.

Remember, even if there are NO Fault Codes or FF Data to offer CLUES of the cause of the symptoms, viewing Live Data, such as Pump RPM, Voltage & Amps Draw, MAY offer clues. Activation of a motor MAY offer clues such as "Speed Deviation", where Actual pump speed does NOT meet "Target" speed requested by DME (as "Triggered" by Tool with engine OFF). Always TEST wiring/ connectors BEFORE throwing parts.

There are MANY different things that can cause your symptoms, so:
DON'T GUESS. DIAGNOSE.
George