Need a Favor Please - Run this Test

[CosmosBlack]

Hi All...

I need a favor please. If you would please run this little test on your car and let me know what happens. I don't know if it only applies to the e39, the v8's or all BMW's.

On my 2000 540i, with the engine running in "Park", if I step on the accelerator and bring the rpm up slowly, anywhere from idling to under 2000rpm, the engine will kinda "stumble" slightly (like rough idling). I was told by the mechanic that this is normal when the engine is running without load.

Ever since I replaced the Throttle body and the Mass Airflow sensor, the engine runs good and the idling is super smooth without missing a beat. I just find it hard to accept or believe that it is normal for the engine to stumble when running in between idling and 2000rpm without load. I tried this same procedure on my Isuzu Axiom and it runs smooth. I remember doing the same thing to my previous Mazda 626 and it ran smooth.

So...if you all would please try this out on your cars and let me know if they behave the same way, I would be able to sleep better.

Thank you!

 

[Trev]

I don't know if this will help, but I do *not* experience this with my '98 528i. I believe you could set a glass of water on that engine, bring it up to 5000 RPM, and there wouldn't be a ripple in the water.

Best..........Bob

 

[CosmosBlack]

Well, it runs fine from 2000rpm upwards. So 5000rpm is fine.

You're supposed to try to hold it steady anywhere from above normal idling to below 2000rpm. If none of you experience some slight "stumblling" in this "accelerated idling", (especially in a 540) then I know something's not right with mine!

Thanks!

 

[Trev]

Can't help with the 540 part, but I can run it smoothly and steadily at any RPM from low idle to as fast as I dare with no load on it. That's what "bring it up to 5000 RPM" meant.. any speed up to there, above which I don't care to go in neutral, and no vibration.

Just trying to help.

 

[bahnstormer]

shouldnt really rev an auto like that....no input on your topic though sorry

 

[Dinan55]

My 528i is a manual, sorry.

 

[j2azz]

It's the oxygen sensor. Its a bigger issue with turbo engines, but it sounds like it can effect NA engines as well. Older turbos (Saabs for example) would have the O2 sensor go, and the idle would be REAL rough. Car would start, rev itself to 2-3k, then drop to almost a stall, rev up again and repeat the process until the car warmed up and it would then at least not stall out.

Mass Air flow sensor was known to do it too. Sort of a combination between components going...

 

[tiger]

I’ve attempted to replicate the same procedure on my 97 528ia with no issues.

I do tend to agree with you. Such ‘rough idling’ should not exist, regardless of load or no load

 

[Wadula]

we have a similar issue, but not when reving up slowly but the opposite. when i hit the throttle real quick and only briefly the engine stumbles and rumbles a bit. i even manages to stall it that way. it is no problem as the engine runs just fine and has passed several tests and inspections. we have that behaviour since the car was build so it is basically stock.

 

[CosmosBlack]

When I step sharply and briefly on the accelerator like you described, it behaved the same way. But it doesn't stall though. It stumbles for a bit, then revs, and on its way down, everything's smooth. It just doesn't respond quick enough like other cars that I have tried this on. On some cars, when you step on the gas, they rev up just like a 2-stroke motorcycle engine!

Does this have something to do with the drive-by-wire compared to the conventional throttle cable, which is more responsive. I mean, you step on the pedal, pedal pulls the cable, engine revs....simple and quick.??? I dunno....

 

[Gib-McFragger]

Yep, when you jam on the throttle, there is a very brief delay while the DME decides if you really meant to do that. The delay is VERY minor and you should hardly notice it after a while, but yea, it's slower to react than a drive by cable.

 

[CosmosBlack]

Thank you, Gib-McFragger. That is a relief! Knowing that I don't have to replace something else! And a disappointment knowing that I'm stuck with this behavior.

But I wouldn't say it's so very minor that I wouldn't notice it. It DOES stumble, then picks up the rev. If I step on it gradually then sharply, it revs up all right. I also notice that when I get ready to pass on the highway, and floor the accelerator, it takes a second before the pull comes in. Compared to my previous e34 540i, that one would pull instantly. Same delay when I step on it from stationary. Wouldn't you say this is a compromise in performance? A step backwards?? What would the advantage be with the drive-by-wire? Please enlighten me...

Thanks!