Off Idle Throttle Response

[Richard in NC]

I've had a frustrating problem with my 650i for quite some time. It seems I noticed it not long after I bought the car (used) but it comes and goes. At first I thought it was unfamiliararity with the clutch but I don't think so now. I'd like some thoughts on it:

First the symptoms: Coming off idle or at low speeds, I get poor throttle response kind of like the engine stumbles once or twice before acceleration comes on smooth and strong by 2500 RPMs. I notice it more when the car is first warming up but today it occurred all the way home. Most of the time, all of a sudden the problem goes away and it jumps out so quick like its in sport mode. I can release the clutch from a stop, hold the throttle at a fixed point and it goes stumble, stumble, and then zoom as if I pushed the throttle another inch. It's then usually good the rest of the drive or at least much less noticeable.
The problem occurs when its warm or cool outside, dry or humid, normal or sport mode, and is noticed in 1st, 2nd or 3rd anywhere below 2500 rpms. Today it seemed worse on a cool humid day.

Its an '06 650i with a 6 speed manual. With only 21,000 miles, I doubt its a fuel filter or plugs, besides its intermittent. I always use 93 octane gas, Exxon mostly, with occasional stops at Shell and BP.

I reported the problem when I had the car upgraded to 25.02. They doubted it would fix it. It didn't. Being intermittent and a minor stumble, it will be difficult for them to reproduce and diagnose.

Does anyone have a similar problem or any ideas?

Richard - Have you ever been able to reproduce this problem for your :bmw: dealer?

[Richard in NC]

I only have had it in for service the one time. They basically hoped 25.02 would fix it but doubted it. I don't think they tried to reproduce it and I didn't have time to hang around. It did seem to run fine that afternoon but has since had the issue. One interesting note is my previous car(E39 M5) LOVED cooler more humid weather and was noticeably quicker but never had a stumble or hesitation at other times. Given that, I'd think on a cooler day like today and other recent days (80 vs 95) the 650i would run better.

[Spyder]

This will be a tough one to diagnose Richard until the problem occurs frequently enough to demonstrate to the dealer, or the car throws a code.

Do you have a trusted BMW indy shop? Usually, they'd be more conscientious sorting something like this out, and then you could take it back to the dealer for warranty repair. In an older BMW, I'd suspect an idle control valve, but without a shop manual (try to get one of those on a new BMW!), I have no idea what piece of software has taken over that function.

Spyder

[cobradav]

:agree: Real hard. Since reprogramming did not take care of it the next best attack from a software point of view would be special coding of the DME. Sometimes an BMW field engineer is called in on especially difficult problems with a laptop and direct coding of the DME.

Now this is if they do not find a hardware problem such as a sensor or Incorrect tolerances and geometry of Valvetronic intermediate levers or similar.