09 35d surging around 2k rpm with light acceleration

[smassey321]

My new to me 09 35d is surging/hesitating when I try to accelerate gently from about 1800 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.

I watched boost with Torque last night 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.

I tried to view throttle position but Torque was not showing it to me. No codes are stored.

[apw2607]

Has it had the emissions recall done? My issues (like the ones you describe) went away once the recall work was done

[smassey321]

It looks like a campaign was done in 2010.

[ingenieur]

More aggressive throttle would seem to indicate the turbocharger and boost control is working - but EGR is also turned off so as to not introduce very hot exhaust gas into the intake.

Try unplugging the HP EGR valve or HFM to see if it is being caused by too much EGR.

[smassey321]

Is the HP EGR is the connector around the DEF on the intake side? The problem is getting worse and I need to figure this out. It runs/hesitates like it is ice cold even though it is fully warmed up. MPG is also getting worse. Also, I checked coolant temp and that is fine.

[smassey321]

Ok I unplugged the HP EGR wiring just behind the throttle. The hesitation is now gone and MPG is back up. Power seems lower than normal which seems odd. Still no codes stored.

[smassey321]

Well I think most of my issue is gone for now. My battery died Sunday night. I removed the battery and left everything unhooked for 12 hours and then installed a new battery. Now it runs like a different truck. The near constant hesitation is gone. MPGs are up. Idrive boots better.

The battery started the x5 fine. The problem was it would die if I sat with the ignition on but the engine not running withing 5-10 minutes.

[bawareca]

Good to hear it is back to normal. It is always highly advised first measure to do a battery reset. Usually leaving it disconnected overnight gives best results. But what you describe is strange. On mine and a few other cars, when the EGR actuator is disconnected the engine will be in limp mode and "Reduced engine power" will be on the display.

[ard]

Does this feel like Windows?!?!?

"I dunno what it was, but rebooted it and its fine....moving on."

[bawareca]

Originally Posted by ard

Does this feel like Windows?!?!?

"I dunno what it was, but rebooted it and its fine....moving on."

Absolutely! Under certain circumstances(like low voltage) the data in the volatile memory(RAM) of a given module gets corrupt and it start acting up. After power off reset all modules boot from the flash memory and many times that cures the problem. In other cases the flash memory gets corrupt and many times reprogramming can fix the problem. Sometimes it is so bad that the module doesnt communicate at all and sometimes it could be fixed by reprogramming the MCU directly. Leaving the battery disconnected overnight or even for 24 hours ensures all electrons are gone from the RAM cells and after reboot all data will be correct. As a matter of fact 24hr battery reset makes a difference than a brief disconnect.
Here is my ICU unit for ECUs that dont feel well