slight surging while accelerating anyone?

[csirisky]

91 525i has slight surging while accel and the fuel milage gauge fluctuates with the surging.......anyone been there?

[632 Regal]

Icv

[cableface]

Icv
Yep, it fixed mine.

[genphreak]

Yep, it fixed mine.Most likley.

Can it not be a bad AFM too- giving the wrong info to the ECU?

[Robin-535im]

91 525i has slight surging while accel and the fuel milage gauge fluctuates with the surging.......anyone been there?
There was a thread on this type of behavior a few months ago, search for surge or surging and see if you can find it.

My last 2 535's have done something similar, under a gentle load like slowly accelerating up a gradual incline, a kind of "stepped" increase in the power with a constant pedal depression. AFAIK all the parts were in working order, it's just something these cars can do from time to time. Others had the same experience.

Nonetheless... it's a good idea to make sure your ICV is clean and working and that you have no vacuum leaks.

[jbourke]

There was a thread on this type of behavior a few months ago, search for surge or surging and see if you can find it.

Yep I started that thread ... anyway it seemed to be caused by either:

a) normal behaviour
b) O2 sensor
or
c) ICV

in my personal order of likelyness. I don't think that the ICV can cause this with higher RPM's but that is probably my limited understanding of engine management systems. If it would be normal behaviour than some expert members on this board can probably elaborate on Motronic AI :D

[NovceGuru]

It was the 02 sensor for me, 93' m50tu.

[cableface]

It was the 02 sensor for me, 93' m50tu.
I had problems with my O2 sensor but it did the opposite for me. The rpm dropped way down when I tried to accelerate, but it wouldnt surprise me if it behaved differently for someone else.

[Robin-535im]

Yep I started that thread ... anyway it seemed to be caused by either:

a) normal behaviour
b) O2 sensor
or
c) ICV

in my personal order of likelyness. I don't think that the ICV can cause this with higher RPM's but that is probably my limited understanding of engine management systems. If it would be normal behaviour than some expert members on this board can probably elaborate on Motronic AI :D

I'd vote for a)... I noticed the exact same (subtle) behavior on two different cars (both 535's), both with slightly different engines (one was rebuilt) but with stock everything else and all parts in working order as far as I know.

The motronic does specify things at discrete points, but it should interpolate between points, not use a "zero-order hold" (looks like stair steps) as they say. The timing advance is set at 50 rpm intervals, I believe. HOWEVER, I doubt it's more than a nearest neighbor interpolation, so the curve will still be continuous but not smooth... i.e. there are crooks in the curve that might be felt if all else is calm and smooth.

Ahhh.. message board pontification... I can toss out theories all day and never have to back it up... :)

[python1]

Yes I have my 1994 525i was doing that until I replaced the oxy sensor and throttle position sensor. Now I just have an off Idle stumble..

pan