S54 stumbling at idle

[nesrevival]

Normal..

[VitaminT]

Mine does it when I am running low on fuel. Otherwise it seems to be fine when I have more fuel and during driving.

I also have it surge pretty strong on cold start but chocked both of these up to "normal".

[intoflatlines]

This happened to me multiple times yesterday. It was hot and my fuel light was on. Filled up and we'll see if it happens again.

[just2talented]

Originally Posted by elwesso

Mine does that right after I start the car.. It will crank, run for about a second, then rpms will dip down. Sometimes it does stall, but once it's going it runs fine. If I hold the throttle open about 1/4 when I crank it, it doesn't do it at all.

WHS

I get that all the time. I always give my car a little gas when i start it after sitting awhile. Just a little bit of pressure on the pedal is all you need. Dont flood your engine.

[XMetal]

Thanks for the low fuel observation...I'll make sure to note whether it's related to low fuel in the tank the next time this occur.

[DerrickO]

For those of you following this thread, I'm pretty sure I've solved my rough idle issue with my 2006 M Roadster and though I'd share what was wrong and what was done to fix it.

Since around 75,000 miles, I've been experiencing a highly intermittent issue where the car would only have a rough idle (after driving for an hour or so) when stopped at a stop light.

Normally when stopped, the tach needle would be just under 1,000 RPMs and the needle would be steady. When the rough idle happened, the car felt like it was struggling to stay cranked and the needle would gently bounce downward into the 500ish range. When this occurred, I would gently tap the accelerator pedal to get it up into the 2,000 RPM range and usually it would correct itself and the rough idle would disappear. Sometimes, if I did nothing and just let it sit there, the car would stall out completely.

In March 2015, my car hit 100k. One day, I ran to grab lunch at a place that is about 5 minutes from the office and the drive over there was uneventful. After lunch when I got back into the car and cranked it up, the BRAKE, traction control, and the EML light was lit up like a Vegas slot machine on my dash. The car had gone into "limp" mode and had zero power. I pulled back into a parking spot and shut the car down. I waited 5 minutes and started the car back up and it was like nothing had happened.

For a few years now, I've been taking my M to an independent mechanic and they've been fantastic. Below is the break down of the invoice:

Labor 2.50 hours @ $89.00 / hr = $222.50

13627840537 Throttle Act-S = $662.60
13637840383 Throttle Switch-S = $99.00
17227836830 Connection (Rubber Hose) = $40.32

SCAN FOR ROUGH IDLE - FOUND THROTTLE VALVE ADAPTATION VALVE INOP - REMOVE INTAKE AND REPLACE THROTTLE ACTVATOR ASSEMBLY AND THROTTLE SWITCH ON FRONT OF MOTOR - CLEANED THROTTLE BODIES AND REINSTALLED INTAKE MANIFOLD CLEARED FAULTS

It took almost 3 weeks to get my car back, as the $40 rubber hose was only available in Germany. My mechanic said that I really didn't need it, but I didn't want to take any chances and wanted every single thing that could be causing the problem replaced.

Now that I've had the car back for a few weeks now, I'm happy to report that the problem hasn't resurfaced and it is like new again.

One of the biggest things I've noticed after the throttle service work is that SPORT mode is now a lot better in stop & go traffic. For whatever reason, I never connected the rough idle problem and the fact that 1st gear was almost un-drivable (stalling out) with SPORT mode on.

[XMetal]

Thanks for your comments and solution on the subject, much appreciated.

This is definitely a weird issue for all of us. My car had been doing this since 8K or 9K miles and is totally random as to when it occurs. I've only had a stumble once or twice since starting this thread and the car is currently at about 38K miles. No codes being thrown either.

[yousefnjr]

Have the rough idle every once in a while, and had a couple stalls too. One time it went into limp mode with the EML light on as described above. It was right after I filled up the gas tank, and I was rolling down the street in 3rd gear. I was coming to a turn, so I down shifted to 2nd and blipped the throttle to rev match. As soon as I hit the gas pedal to blip, thats when it went into limp mode with all the lights on the dash. I turned the car off and restarted it, no issues. Pulled back into work and scanned for codes and there was nothing Hasn't happened again since

Intrigued by throttle actuator replacement. I remember reading the gas pedal itself causing issues for some people. I notice that sometimes my throttle feels sharper and the car feels faster than other times. Maybe there's some common thread here somewhere.

[bosstones]

I've only ever noticed it when I first take it out of winter storage or if it has sat w/o being driven for a while. It is its way of showing its displeasure for not being driven.