For a while now my z has had an issue with running when cold.

It was partly solved when I had the aav replaced, but not completely.

The garage that did the work said that problem may be down to the ecu?

I did borrow a ecu and try to see if it made a difference but it didn't.

I'm starting to think that the garage didn't realize the zed had a separate ecu for the fuel pump and was wondering if this may actually be the issue.

Before the aav was replaced the revs dropped right down from start up.

Now it last for about 30 seconds until the revs drop.

Once the engine is warm, it runs fine.

Also, I've notice that the fuel pump is humming louder when the revs are low.

Question is...

Is this issue down to the fuel pump ecu or the fuel pump itself? Or is it something completely different?

No one have any idea then?