What causes a slight jerking / stuttering / surging when letting off throttle?

[CamE32]

I've done a lot of searching, and the only posts I can find are related to hesitation/stuttering under acceleration. The problem I've been experiencing since I got my 735i on the road is a jerk or stutter every time I let off the throttle. It's buttery smooth on acceleration and responds instantly to throttle input... but it feels like for a fraction of a second it wants to stall when I let off the throttle (specifically, JUST when the throttle is all the way closed and the switch in the TPS senses idle). You can feel it in the car because it surges after letting off the throttle for a brief second, I assume when the ICV opens more to keep it from stalling out. To clarify, it's not really noticeable unless you're driving over 15-20mph.


I've swapped ICV's, tested/adjusted the TPS, tested/cleaned the Crank Position Sensor, and installed a new DME coolant sensor.



I'm leaning towards a vacuum leak somewhere other than all the hoses I've replaced (valve cover maybe?). Any input is appreciated!

[Timm]

Yes, that could be a vacuum leak - but it is also classic symptoms of a tired MAF. If you can get diagnostics working you can work out which one it is:





https://www.meeknet.co.uk/E38/Diagnostics.htm

[CamE32]

Thanks for the reply!! I swapped in the MAF from my parts car and it made no change. In fact, the one from my car is in better condition but I couldn't tell a difference between the two when driving.

MAF2.jpg MAF1.jpg


To give some more info: the problem I'm experiencing only really presents itself when I'm going over 30mph and let off the throttle. All is well until the last couple millimeters when the TPS idle switch is triggered (and the throttle body is closed I suppose), then the engine surges (most noticeably at 1500rpms) and misfires at higher speeds/engine rpms. What confuses me is how smooth it is getting back on the throttle. Additionally, the engine rpms dip on recovery when I quickly open the throttle manually under the hood...

I also hear a whining from somewhere near the front of the engine that dissipates as the car warms up... but still audible when opening/closing the throttle with the hood open. So with that in mind, I think I need to find someone who will do a smoke test and illuminate any hard to find vacuum leaks (intake manifold, valve cover, what else?).