540i Bounces Off Base Idle

[wmrcs]

Hey guys, ever since I swapped my 530iT with a B40/6 I've noticed that when I put the clutch in the idle will drop down to ~500 or so and stick for half a second and bounce up to about 750 rpm before settling at it's normal idle (probably 600ish). I do have a lightweight flywheel, 255LPH fuel pump, and a DUDMD chip, other than that it's stock.

In the last 6 months or so it has stalled out maybe 3 times under the same circumstances. Always starts back up fine and never get a CEL. Any ideas?

[Mykk]

See if DUDMD will raise the idle a bit in your tune. Lightweight flywheels need a couple hundred RPM more to maintain idle. My 540i/6 with a 17lb aluminum flywheel stalls at anything below 800rpm.

Also, did you add the UUC recommended blend of Redline 75W140NS & D4 ATF to prevent internal trans gear clatter at idle? If so, like me. The RPMs will drop with the clutch engagement due to increased oil resistance in the trans.

[BleedsBlue]

^Those are definitely good things to check, but also never write off the simple, stupid stuff like a torn intake boot, until you check.

[wmrcs]

See if DUDMD will raise the idle a bit in your tune. Lightweight flywheels need a couple hundred RPM more to maintain idle. My 540i/6 with a 17lb aluminum flywheel stalls at anything below 800rpm.

Also, did you add the UUC recommended blend of Redline 75W140NS & D4 ATF to prevent internal trans gear clatter at idle? If so, like me. The RPMs will drop with the clutch engagement due to increased oil resistance in the trans.

Oh, I didn't realize that the idle needed to be raised. I will contact him and see what he can do -- my flywheel weighed in at 15.2 lbs. And NO I did not, I don't even remember exactly what I put in the trans right now, I'll need to refer to my build thread but I DEFINITELY have some clutch/gear chatter... really bothers me at times. What is the blend ratio of the oils?

^Those are definitely good things to check, but also never write off the simple, stupid stuff like a torn intake boot, until you check.

Yea, I've already perused around for vacuum leaks and didn't find anything. Although, I do need a new intake boot soon.

[BleedsBlue]

Although, I do need a new intake boot soon.

Why do you say that? I mentioned it because your symptoms were identical to mine when I had a degraded intake boot, but I didn't have the LWFW in the equation either, so I didn't want to sound cocksure

[wmrcs]

I somehow lost the rubber gasket/seal that is rather secured in the air box side of the boot and I secured the clamp down hard. It split the boot where I tightened it up, but I was able "choke up" on the air box with the boot so it's still pretty sealed. I delicately remove the air box now out of worrying I won't get the boot to secure back onto the MAF haha. I was already having this issue though prior to my intake boot shenanigans, BTW.

DUDMD got back to me about raising my idle. He said he wasn't sure if he was actually able to raise me idle but that the stalling was indeed due to my lightweight flywheel... dafuq am I supposed to do about it then!

[wmrcs]

Just checked back on my swap thread and I used RP Synchromax in the trans. I remember reading a lot of great reviews about that in the 420G, but I'm definitely going to order up a quart of 75w140NS and D4 ATF asap. My gear rattle is pretty obnoxious after the trans heats up.

[Mykk]

http://store.uucmotorwerks.com/artic...uce_rattle.htm

In my experience it has totally stopped gear rattle, but it's now tougher to get the syncros to line up for quick shifts and I can feel a bit more parasitic drag in the trans.

[wmrcs]

The noise is just too much for me though on a warm day of gleeful shifting. What is your idle set at Mykk? Are you tuned?

[Mykk]

My set up is different. I deleted the IAC and my idle rpm is set by the throttle blade stop screw.

With the lightweight flywheel and after dialing in my own cam timing I have idle rpm around 850-900. That's where it gives me the least amount of problems.

I use an ostrich 2.0 in a 404dme. I have a DUDMD tune he sold me and I load it on the ostrich. But I've also taken an OE bin and made my own xdf for tunerpro and experiment around with my own tunes.

[BruinBimmer]

http://store.uucmotorwerks.com/artic...uce_rattle.htm

In my experience it has totally stopped gear rattle, but it's now tougher to get the syncros to line up for quick shifts and I can feel a bit more parasitic drag in the trans.

Just to add some color here, UUC references another article in that article: http://store.uucmotorwerks.com/uuc/a...ear_rattle.htm

Basically, they say that using a sprung-hub clutch design with a single-mass lightweight flywheel reduces rattle as well. I did not see the OP mention an aftermarket clutch, so I assume he has an OEM solid center clutch. I believe moving to a sprung-hub clutch would help.

FYI, I am running JB Racing 13lb flywheel and a Conforti chip (no idle change IIRC). I had this done when the clutch went out around 140k mi, so I had a Clutchmasters FX100 thrown in there at the same time to cut labor costs. Thus, I do not have before/after sprung-hub clutch feedback with the LWFW to prove the article's accuracy. But I can say that with this setup and RP Synchromax (not the UUC recommended blend), the only time I ever hear rattle is low RPM + high load (e.g. maybe 1500 RPM + >50% throttle). This is rare, since you'd normally change down a gear anyways.

Best of luck OP, hope something in this thread works out for you.

[wmrcs]

Just to add some color here, UUC references another article in that article: http://store.uucmotorwerks.com/uuc/a...ear_rattle.htm

Basically, they say that using a sprung-hub clutch design with a single-mass lightweight flywheel reduces rattle as well. I did not see the OP mention an aftermarket clutch, so I assume he has an OEM solid center clutch. I believe moving to a sprung-hub clutch would help.

FYI, I am running JB Racing 13lb flywheel and a Conforti chip (no idle change IIRC). I had this done when the clutch went out around 140k mi, so I had a Clutchmasters FX100 thrown in there at the same time to cut labor costs. Thus, I do not have before/after sprung-hub clutch feedback with the LWFW to prove the article's accuracy. But I can say that with this setup and RP Synchromax (not the UUC recommended blend), the only time I ever hear rattle is low RPM + high load (e.g. maybe 1500 RPM + >50% throttle). This is rare, since you'd normally change down a gear anyways.

Best of luck OP, hope something in this thread works out for you.

Thanks for the input. I am using an OEM E39 M5 unsprung clutch disc. My clutch chatter is rather minimal but it is there at a hot idle, that doesn't really bother me like the trans rattle does when hot, though. I have never used 6th gear out of necessity haha I have only used it simply "to use it" because with the 2.81 rear diff, my RPMs are below 2k even around 70 MPH. If I give it 50%+ throttle in 4-6 gears under ~2k RPM my trans chatters aloud. I will be doing the UUC mixture especially with summer around the corner. If for whatever reason I need to pull the trans I will add a sprung clutch disc and document the difference.

- - - Updated - - -

Oh, I've never heard of deleting the IAC. Did you document this in your thread? I'm curious to learn more. I would love my hot idle to be around 800 or so, I would likely have no more clutch chatter while idling at that speed and wouldn't even need a sprung hub clutch. Wow, that's a cool set up! Have you dyno'd it? Have you experimented with any FI tuning on the M60?

[Mykk]

Oh, I've never heard of deleting the IAC. Did you document this in your thread? I'm curious to learn more.

I'd encourage everyone to keep them clean & functional and not remove them completely.

[BruinBimmer]

I'd encourage everyone to keep them clean & functional and not remove them completely.

Yeah, it sounds like your setup would lose idle consistency across different temperatures/elevations/etc