Engine Rough at Low RPM

[CosmosBlack]

If I have the engine running with my car stationary in "park" position, I step lightly on the accelerator pedal and hold at anywhere above smooth idling and below about 2000rpm, the engine kinda "flutters" (don't know the exact word to describe it). It's like you can feel very minute misfirings, or as if there is this "bubbling" feel like in the old engines running with the choke lever on. When I step on it more and bring the rpm up past 2000, it runs normal.

Same thing when the car is running in gear and moving from stationary or cruising slow below 2000rpm, except that I don't feel it that much unless I pay close attention to it.

Has anybody experienced this before? Is this normal, I don't think it is.
It might have something to do with the "Service Engine Soon" light that is on now and that I'm trying to figure out what the fault is. DIS showed a vague "fuel mixture too lean or rich" problem. I had just replaced a faulty oil separator and thought that was it, but the light came back on. [???1]

Thanks.

By the way, it's a 2000 540iA

 

[MrElussive]

Take it in for service ASAP, it could be a serious mis-fire problem.

 

[Marinakorp]

bet its the MAF sensor

 

[ILuvBMW]

Something similar happenned to me. The engine seemed to misfire a tiny bit and the car would very very very slightly 'bump', and the check engine light was on. It ended up being a chip that needed replacing for some reson.

 

[CosmosBlack]

Thanks all for your response and input! I have an appointment this Thursday to run the car on the DIS again, and I'll post the solution here later, if they do find the culprit this time.

Marinakorp,
What is a MAF sensor?

 

[Marinakorp]

Mass Airflow Sensor


could also be the CPS (Camshaft Position Sensor)

if the car is under CPO - they are covered... the MAF is like... 400 or so... the CPS is 30 or so


If out of warrenty - replace the CPS (not too expensive) then the MAF (expensive)


By running too lean... might be the air fuel mixture (MAF) is wrong... the incorrect information is being sent to the OBC (on board computer) and messing things up...

on the other hand... they could also be referring to the O2 sensors (pre cat (catalytic)) - sometimes these codes are "mysterious" and sometimes not

 

[tiger]

I can help by telling you it's not a CPS (Cam Position Sensor). I just had that problem and the engine did not respond in that fashion.

At any rate the cost I incured for the CPS was 180 ( $90 Part + 85 labor)

 

[Marinakorp]

Great - cross that off the list!


The CPS is really an easy part to DIY - check www.bmwtips.com


Didn't realize that it was 90 for the part... seems a bit high

 

[CosmosBlack]

Guess what? I was at my mechanic's today and was told that I need a new Throttle body/valve. The symptom/fault has something to do with the engine trying in vain to search for an idling speed at low rpm's, but when it goes faster at higher rpm's it goes out of idling mode and so seems to be fine. (If I understood him correctly!) Anyway, it's an expensive part, gonna cost about $600 and $130 labor to install it. I also have an option to install a Dinan part which I was told will add about 8 to 10 hp to the performance.

Does it make sense at all?
Any feedback or similar experiences?
I will be given several pricing options tomorrow before the parts are ordered.

 

[tiger]

Unfortunately, many diagnostic faults produced by the computer will trigger the ‘Does it make sense?’. I’ve been there before, many times. You just have to trust the computer and diagnostic. I never guess anymore sense every time it’s a new learning experience.

Cheers…

 

[CosmosBlack]

I think they fixed it!

Marinakorp, you were right on the money!

Yesterday I had the throttle body replaced ($390+) and the light came back on after I drove off from the shop. Brought it in last night and dropped the car off so they could have a cold engine to work with this morning. Replaced the Mass Airflow sensor ($490+). So far, no lights. I hope we got the culprit. The engine idles very smooth now and flooring the accelerator is very responsive.

My mechanic said he switched the old throttle body back in to see if it'll work but the light came back on and there was some "flutter" in the idling. I guess it's a combination of both faulty parts.

 

[Marinakorp]

Congradulations on the FIX!


Should feel like a whole new car!

 

[CosmosBlack]

Not so good!

I was coming out of an exit into the Interstate the other day, I floored the accelerator and zoomed right across to the fast lane, doing about 80mph, when the engine suddenly stalled. Had to pull over by the emergency lane off the fast lane, what an embarrasing moment! The engine wouldn't start.

Anyway, mechanic came and read the error code as fault from the Air Mass sensor heat film! NOT AGAIN!!!! It's brand new, less than 2 weeks old! And it was an OEM part from the dealer!
What kind of quality product (Bosch) is BMW coming up with??? At first the mechanid refused to believe the error code, he kept repeating "It's impossible!" So, they still had my old Air Mass sensor in the shop, he called somebody to run it over, put it on, and the engine started up!

Well...good thing parts and labor are under warranty. Bad thing is, the next time I step on it, I can't help but fear that I might get another surprise.

 

[Marinakorp]

Do you have an aftermarket Air Filter (K&N, or otherwise)?

 

[CosmosBlack]

No I don't, everything is basically stock. Just went in to the dealer today to replace the faulty MAF sensor. Hope everything works fine from now. I got the old sensor in my trunk just in case!

Another bad news, they told me today that I need a new seat memory module to reprogram my keys! My steering wheel keeps going out of memory setting everytime I arm and disarm with my key remote. So I have to press the memory button after unlocking my car! Only the steering goes out, the seats and mirrors remain in memory. I tell you...BMW and their electronics sucks. I don't think I'm gonna spend $200 on that issue. I'm gonna adjust my seat settings to suit the damn steering position! Maybe the module might go cuckoo one day and work right again!