Rev Hunting on Cold Start (N52)

[Mach1er]

Alright guys, I got 6 new coils a few months ago and ever since then the RPMs fluctuate a bit on cold start. It didn't do this at all prior to the new (Delphi) coils.

I figured maybe the engine had to re-adapt to the coils, so I didn't bring it in right away, but 4-yr warranty is up in a couple of weeks, so it's time.

Any thoughts on what this could be? Bad coils, need to reset the engine adaptation, need new plugs, they dropped something in during coil replacement?

https://youtu.be/-sO8rgNHxvU

[HawkeyeGeoff]

Originally Posted by Mach1er

Alright guys, I got 6 new coils a few months ago and ever since then the RPMs fluctuate a bit on cold start. It didn't do this at all prior to the new (Delphi) coils.

I figured maybe the engine had to re-adapt to the coils, so I didn't bring it in right away, but 4-yr warranty is up in a couple of weeks, so it's time.

Any thoughts on what this could be? Bad coils, need to reset the engine adaptation, need new plugs, they dropped something in during coil replacement?

https://youtu.be/-sO8rgNHxvU

[u2b]https://youtu.be/-sO8rgNHxvU[/u2b]

This is typical of a vacuum leak. Take a look at all the vacuum lines going to the intake mani, intakes, and valve cover.

If you have a JB4, torque app, or something similar a quick glance at this would probably show a very positive short term fuel trims that could confirm it.

[Mach1er]

Originally Posted by HawkeyeGeoff

This is typical of a vacuum leak. Take a look at all the vacuum lines going to the intake mani, intakes, and valve cover.

If you have a JB4, torque app, or something similar a quick glance at this would probably show a very positive short term fuel trims that could confirm it.

Thanks, I'll check torque in the morning.

[needexhaust]

Having same issue except on warm starts, let me know if you figure it out!

[Bimmer-Bob]

Originally Posted by Mach1er

Alright guys, I got 6 new coils a few months ago and ever since then the RPMs fluctuate a bit on cold start. It didn't do this at all prior to the new (Delphi) coils.

I figured maybe the engine had to re-adapt to the coils, so I didn't bring it in right away, but 4-yr warranty is up in a couple of weeks, so it's time.

Any thoughts on what this could be? Bad coils, need to reset the engine adaptation, need new plugs, they dropped something in during coil replacement?

https://youtu.be/-sO8rgNHxvU

[u2b]https://youtu.be/-sO8rgNHxvU[/u2b]

Did you try to pull for any codes?

[Mach1er]

Originally Posted by Bimmer-Bob

Did you try to pull for any codes?

Yeah, no codes thrown.

[Mach1er]

Update (HawkeyeGeoff) :

Below is the screenshot of what my short term fuel trims look like during the rev hunting. During normal start, that's a pretty smooth line. Clearly not so in this case. So far, dealer techs haven't been able to find anything. They will try again Monday. This 320i loaner is a snooze.

[Mach1er]

Update: Bringing her home tomorrow. Dealer couldn't reproduce, and couldn't find anything wrong. Shop foreman watched the video and says this could be "normal" and I don't buy it. Either way, not much I can do at this point.

BMW Platinum Extended Warranty kicks in on Friday.

[WDE82]

Probably not normal but probably not a big deal anyway. Could be many different things. Just let it be. It will probably go away TBH.