S54 cold start issue!

[argenta]

Well hello!

Owner of a 2006 Z4M Coupe here, 206000km, slight cold start, tick-over issue:

As long as the air-plus system is on (first 30-40sec) the engine vibrates somewhat, like a slight misfire.
Once it turns off, its smooth as silk, running normal.

This started about 10000km ago, gradually gotten worse.

Whats this?

Done compression test, leak-down test, cleaned all injectors, new sparkplugs, changed all coils, checked the function of the air-plus valve. Everything is good.

[grannyknot]

I think you are talking about the secondary air pump that improves emissions for the first minute or so after start up?
If so, I would check the pump to make sure it is working properly, also the valve that is mounted centrally, the right side of the engine on the head.

[argenta]

Yeah as I wrote, those things are checked & clear.

[grannyknot]

Hmmm, the only other thing I could suggest is unplug the pump and see if it makes a difference.

[AK72]

I would scan car to begin with, also at your mileage I would clean clean Idle control valve and throttle bodies

[argenta]

Two good replies, thank You!

Off to buy some pliers.