[smass]

Recently I sold my 06 330 and picked up a 09 X5d. I asked this question in the X5 area but you E90 people are far more into this than they are . The X5 is perfect except for a hesitation around 1500 - 2000 rpm during light acceleration. This only happens when I try to accelerate gently from about 1500 rpm up. About 2 surges per second. More aggressive acceleration feels normal but a light press of the pedal can produce the surging in all gears now. This gets odd at around 88 mph when the surging becomes constant and begins rocking back and forth about once per second. The issue is getting worse every day and sometimes results in bucking back and forth within the drive train.

I watched boost with Torque and it is all over the place when this is happening. Mostly in the 15 to 20 psi range but probably going back and forth between the two several times per second. A graph shows a very lumpy sideways S. Not accelerating or more aggressive acceleration show a flat boost line. Torque shows full 23 psi of boost during more aggressive acceleration. No codes are stored. Unplugging the EGR valve electric connector makes the problem go away however power is much lower so that may not be a good test.

[Yozh]

Looking at boost and CBU issues is a default approach, but you should also look at the driveline. Specifically, the universal joint (guibo). A worn joint will produce driveline slop that is what you potentially are experiencing at light accelleration/deceleration

[Hoooper]

Check out the manifold pressure sensor, maybe try pulling it and cleaning it. Boost shouldnt fluctuate that quickly with our setup, to fluctuate several times per second by 5 psi sounds like its getting a bad reading, which would cause hesitation due to the computer getting a screwy boost reading.

[kiel_dafo_kenyg_as]

Originally Posted by smassey321

Recently I sold my 06 330 and picked up a 09 X5d. I asked this question in the X5 area but you E90 people are far more into this than they are . The X5 is perfect except for a hesitation around 1500 - 2000 rpm during light acceleration. This only happens when I try to accelerate gently from about 1500 rpm up. About 2 surges per second. More aggressive acceleration feels normal but a light press of the pedal can produce the surging in all gears now. This gets odd at around 88 mph when the surging becomes constant and begins rocking back and forth about once per second. The issue is getting worse every day and sometimes results in bucking back and forth within the drive train.

I watched boost with Torque and it is all over the place when this is happening. Mostly in the 15 to 20 psi range but probably going back and forth between the two several times per second. A graph shows a very lumpy sideways S. Not accelerating or more aggressive acceleration show a flat boost line. Torque shows full 23 psi of boost during more aggressive acceleration. No codes are stored. Unplugging the EGR valve electric connector makes the problem go away however power is much lower so that may not be a good test.

Rocking back and forth is exactly how the car feels when a dpf regen is in progress. The rocking can be felt most at 2000-2500rpm

[smass]

Originally Posted by whiteblue

Rocking back and forth is exactly how the car feels when a dpf regen is in progress. The rocking can be felt most at 2000-2500rpm

That makes sense as the rocking is more intermittent (less than 5% of the time) than the hesitation (50+ % of the time).

[dixy2k]

back pressure sensor and boost solenoid need to be checked out. At least to rule them out. And yes, everything else mentioned above.

[smass]

Originally Posted by Hoooper

Check out the manifold pressure sensor, maybe try pulling it and cleaning it. Boost shouldnt fluctuate that quickly with our setup, to fluctuate several times per second by 5 psi sounds like its getting a bad reading, which would cause hesitation due to the computer getting a screwy boost reading.

Thanks Hoopper. I think we have a winner. I finally got to pull the manifold pressure sensor last night and it was not that dirty. It had some black goo in it which I cleaned out with rubbing alcohol. This morning on the drive to work nearly all of the hesitation was gone. The first change I noticed was I can now easily maintain the gap between the car in front of me. In the past I was constantly making adjustments which were always too much or too little. I reset the MPG and got 26 MPG for my mostly highway drive to work (I am in FL so it is still summer here). Last week I was not able to get above 21 MPG with an identical reset/drive.

[NickTheStick]

Im experiencing something similar on my 12' X5D. Havent had the chance to poke around, but I may take a look at the same thing. Good looking out!