Fluctuating Idle on Warm Start

[AWE46M3]

On the cold start, I have no idle fluctuation. Car warms up with a steady idle.

On warm starts, I've noticed my idle fluctuates and is a little choppy. It levels out once I begin driving the car and is steady shortly thereafter - just a little chopping on the initial start.

Is this common behavior for E46 M3's, or is there a known issue I might be unaware of? My research has led me to the ICV, TPS, or O2 sensors. Wanted to check here before I start throwing parts at this.

Running a Magnaflow catback exhaust temporarily. Stock tune. No faults or error codes.

Thanks in advance for your feedback.

[02_lsb]

https://www.bimmerworld.com/Intake-Fuel/Fuel-Filters/Genuine-BMW-Fuel-Tank-Breather-Valve-13907831770-E46-M3-E85.html

[AWE46M3]

https://www.bimmerworld.com/Intake-F...46-M3-E85.html

Thanks for your feedback. Mind elaborating why you believe this may be the issue? I am not registering any faults or CEL’s

[Mr.wReckless]

After putting airbox and cams on my car, it always fluctuated at idle. Hassan finally tuned this out, stating that when temps increase the fuelling wasn't correct so it was always trying to hunt and correct itself until he tuned in more fuel.

If your car is fairly stock I would wonder whether your injectors are clogging up and restricting flow? Or maybe a dirty MAF? IDK.

Regards

[sapote]

Thanks for your feedback. Mind elaborating why you believe this may be the issue? I am not registering any faults or CEL’s

I doubt the evaporative valve is leaking as this would trigger the fuel tank leak detection code.
I would use the VeePeak and OBDFussion to get a log with hot idle with these data: MAF rate in g/s, LTFT, STFT, fuel system status 1 and 2, intake air temp, coolant temp, rpm, pre cat O2 sensors, ignition timing. The logged data can reveal the root cause.

[AWE46M3]

After putting airbox and cams on my car, it always fluctuated at idle. Hassan finally tuned this out, stating that when temps increase the fuelling wasn't correct so it was always trying to hunt and correct itself until he tuned in more fuel.

If your car is fairly stock I would wonder whether your injectors are clogging up and restricting flow? Or maybe a dirty MAF? IDK.

Regards

Thanks for that context. I am running an aftermarket catback on a stock tune. Higher flow than stock - wonder if that is contributing to it.

I doubt the evaporative valve is leaking as this would trigger the fuel tank leak detection code.
I would use the VeePeak and OBDFussion to get a log with hot idle with these data: MAF rate in g/s, LTFT, STFT, fuel system status 1 and 2, intake air temp, coolant temp, rpm, pre cat O2 sensors, ignition timing. The logged data can reveal the root cause.

Awesome - this is exactly what I needed. I’ll test those systems and take it from there. Thank you 🤝

[02_lsb]

I don’t have expert opinion but I can tell you what happened with my car. Over the course of a year, I’d have intermittent warm idle issues, without codes. One day, the code finally showed up and it was for the part number I shared with you.

[AWE46M3]

I don’t have expert opinion but I can tell you what happened with my car. Over the course of a year, I’d have intermittent warm idle issues, without codes. One day, the code finally showed up and it was for the part number I shared with you.

Appreciate it - thank you.

[sapote]

I don’t have expert opinion but I can tell you what happened with my car. Over the course of a year, I’d have intermittent warm idle issues, without codes. One day, the code finally showed up and it was for the part number I shared with you.

To pin point if the bad fuel evaporative valve is the root cause, I would pull off output hose (the larger of the two hoses) and plug it so zero gas leak can change the mixture. Leave the valve connected to the input hose and cable connector to avoid error code. If problem not change then it's not the valve.

[AWE46M3]

To pin point if the bad fuel evaporative valve is the root cause, I would pull off output hose (the larger of the two hoses) and plug it so zero gas leak can change the mixture. Leave the valve connected to the input hose and cable connector to avoid error code. If problem not change then it's not the valve.

Thank you - you've been so helpful with all my summer issues. Appreciate you.

[Amos]

So my car has had the same issue since I got it 14 years ago and it has not gotten worse or better, it's very intermittent as well.

Since I got the car, I have replaced various parts, I'll name a few that may be relevant. I've basically given up on this issue

MAF
Fuel pump
All spark plugs and coils
Fuel filter
Cleaned ICV but not replaced
Cleaned throttle bodies
Installed Evolve intake
Removed and coded out cats and rear O2 sensors
All belts, tensioners, pulleys, water pump, alternator etc


Maybe it helps you find where to look. I'm doing pre cat O2 sensors next, they are pretty old now.

[AWE46M3]

So my car has had the same issue since I got it 14 years ago and it has not gotten worse or better, it's very intermittent as well.

Since I got the car, I have replaced various parts, I'll name a few that may be relevant. I've basically given up on this issue

MAF
Fuel pump
All spark plugs and coils
Fuel filter
Cleaned ICV but not replaced
Cleaned throttle bodies
Installed Evolve intake
Removed and coded out cats and rear O2 sensors
All belts, tensioners, pulleys, water pump, alternator etc


Maybe it helps you find where to look. I'm doing pre cat O2 sensors next, they are pretty old now.

Thank you for sharing all of this feedback. I am doing EU headers and SS catted section 1 and some point this year (waiting for my SCZA section 3 to arrive that I ordered in March...lol). I plan on replacing O2 sensors at that time to have a fresh set to go with the new cats. Please circle back and let me know if you notice any improvements. I plan on cleaning throttle bodies and doing an ICV cleaning when I do my CSL airbox next summer after I smog the car.