Rough Idle N52 E85 - No error codes

[casper355]

Hello, I have a problem with my Z4 3.0si with the N52 engine and 265 HP fand was hoping to get some help here.

On cold starts, the idle speed is not stable. It is fluctuating quite a lot within a range of +/- 400 RPM.
This is happening already for a long time and is only on cold start and will go away after a short time (+/- 40 sec) when keeping it on idle. When starting, and then immediately go to drive and then keep the engine on idle, the idle is most of the time stable. When the car is not completely cold anymore, it runs perfect. I always use octane 98 fuel.

I already changed some parts to try to fix it. There are no error codes present in the car, also when reading out with BMW software.

I changed the following components not too long ago and didn't had effect on the car:
- 6 NGK spark plugs
- 6 Bosch coils
- 4 Bosch O2 sensors
- Fuel injectors tested and cleaned (passed the test)
- Fuel pressure regulator (including filter in the tank)
- 2 new original camshaftsensors
- cleaned both Vanos solenoids
- cleaned both Vanos filters
- checked oil filter housing for O-rings
- new starter
- new battery (Varta, 2020)

I was hoping someone here could point me in the right direction? Or share your solution if you had the same problem.

[3002 tii]

Always tell folks, hard to diagnose blindly. Pull codes first.

[casper355]

As already said, there are no codes stored.... That is what makes it difficult to diagnose.

[thalastdon1985]

Spray brake cleaner or carb cleaner around your oil filler cap with engine running and see if it changes the way it runs when you do. Perform same test along intake manifold flanges, disa valves, and any crankcase breather hoses and connections.

[casper355]

Thank you for your reply.
I already tried that but it made no difference.

[thalastdon1985]

Alright. I would try looking at temp sensor data via obd since it seems isolated to cold start.

[Westersund]

A lot of stuff done, but not the most obvious one. Idle control valve or the secondary air pump (emissions garbage).

[casper355]

Thank you both for your replies.

thalastdon1985 I checked this but the temperatures are realistic.

Westersund I Think the N52 doesn't have either one of them?

[Westersund]

Would you look at that! Learned something new today. Valvetronic engines doesn't have an ICV because the valvetronic controls the idle.

The reasoning behind my idea was that you only have problems with idle when the engine is cold. The engine should have some way to heat up the cats faster like cars with secondary air pumps. I would start there.

Seems like you've used OEM sensors as well so that shouldn't be the problem, poor new sensors is usually the culprit when people cheap out on sensors and still think the problem should be fixed.

[rjahl]

Originally Posted by casper355

Thank you both for your replies.

thalastdon1985 I checked this but the temperatures are realistic.

Westersund I Think the N52 doesn't have either one of them?

Try looking at you MAF sensor.

Failing that, I would take a serious dive into INPA and it's monitoring capabilities. If you know what to look for , It's a very good tool.

[B328iC]

The N52 features Valvetronic (variable valve lift), a lighter block due to the use of a magnesium alloy and an electric water pump (replacing the belt-driven water pump) and a variable output oil pump. The redline was increased from 6,500 rpm to 7,000 rpm, except for N52B25. The N52 uses electronic throttle control and variable valve timing (double-VANOS). Higher output versions of the N52 use a three-stage variable length intake manifold (also called "DISA").

[berdy_wooster]

Did you ever figure out what was causing the issue?

[Mysecondwife]

I experienced same issue… I just don’t worry about it. The shop couldn’t figure it out. Wanted to swap plugs, but I had already done that.