2001 540i "surging"

[bmb527]

Hi all,
I have noticed that when at lower speeds, like under 75 mph, my car has a slight "surge". It is mainly audible, but about a 50 rpm swing on the tach can be seen. It hasn't had any CEL illuminations until this morning on my way home, in the rain. I pulled the codes and it has a P0491 code. This is listed as a SAS fault. I cleared the code, it hasn't come back in 43.4 miles, but the "surging" is still evident.
The surging is completely gone at speeds above 80 mph. Has anyone here had anything like this? Any ideas? I am all ears!!
Bill

[shortedaman]

Injectors?

[meangreenbimmer]

Idle control valve or vaccum leak?

[edjack]

No ICV on a 2001 V8.

P0491 Secondary Air Injection System Insufficient Flow Bank 1. Probably means that the injection valve has packed up.

Doubtful this would cause the surge. The SAS is turned off very shortly after startup. I'd vote for a vacuum leak. Connect your scan tool and watch short term fuel trim whilst the condition occurs. If there's a leak, the STFT should show an increase.

Any pending codes?

[philly98540]

Auto or manual tranny?

[rf900rkw]

I would bet automatic and the torque converter clutch is cycling. Or slipping.

[filon102]

clean your MAF sensor, you can get MAF cleaner from your local auto parts store, takes less than 10 min and its cheap

[philly98540]

I would bet automatic and the torque converter clutch is cycling. Or slipping.

This

[bmb527]

Randy,
Yes, it's an auto. I wish it were not, but with 2 fake knees and lots of pain, a clutch just isn't feasible anymore.
Is this something that a transmission servicing might improve...or should I just start budgeting for a rebuilt transmission?
In the stack of maint. records, it shows the tranny was serviced about 57K ago. Do you think it would be worth a shot?
Thanks!

[rf900rkw]

The fact that it hasn't as yet popped a P074x code is a good sign. The EGS may be reacting to bogus inputs, rather than a slipping trans. The problem is, determining which it is will likely required a trained eye on a good scanner with a highly-calibrated butt in the driver's seat.

[bmb527]

Randy
Why don't you bring your best, most proper scanner...and your calibrated butt to Seattle! Beer food and superbowl partying are on me! But I am rooting for Denver!!!
JK.
Would this be something the dealer would be the best bet or would someone good with INPA be able to help diagnose? It is running just fine...it is just not perfect.
I have the software...just no laptop to put it on at the moment...and I don't know how to work the software even if it was ready to go.
Thanks for your input. I was hoping you would stumble upon this thread!!

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On this note...is there anyone in the Seattle area that knows their way around their scanner that would be willing to take a look? I am more than happy to pay for the time...and tutoring.