Despite near-flawless operation over the past few months, I've noticed odd low-speed behavior in our X3 xDrive28i. While accelerating gently from rest, like on a residential street littered with stop signs, the X3 pauses and then slowly starts moving forward. Then you feel the transmission kick down and, after a jerk, you finally accelerate at a normal pace. It never feels like there's a one-to-one relationship between the pressure you apply on the throttle and what the X3 does.
Annoyances are twofold: One, you will spill coffee--whether in the cup holder, on the carpet, leather, or your shirt, something's getting stained. Two, the hesitation between when you ask for throttle and when you actually start moving can confuse other motorists. At stop signs, other drivers have mistaken it for me giving the go ahead, and so when they start driving into the intersection, the delay ends and the X3 zooms straight at them.
I visited BMW South Bay, in Torrance, California. After waiting in a brief line, a service advisor, after listening to my complaint, brought out a technician to ride along with me so I could duplicate the issue. The technician listened carefully as we drove along. Offhand, he thought it might be a characteristic of transmission calibration, called "rolling start shift." You see, while decelerating, downshifting from second to first causes a jolt. According to the technician, BMW may have programmed the transmission to hold second gear for as long as possible, avoiding the shudder. He added that he saw it most in newer BMWs with automatics, especially in the 2002-2008 BMW 7 Series (E65).
I'm not convinced that's the issue. To me it feels like a delay in initial throttle application around the 1000-1300 rpm range. The likely reasoning behind this? Fuel economy. Curbing quick (or "jack-rabbit") starts means you burn less fuel.
The tech checked for fault codes and found nothing. Had any TSBs been issued? Nope. He offered to take the car for the day and clear any adaptations it had made to my driving style. I agreed, and the dealership offered a free loaner car. And while the wait was long to get one, it was worth it. The guy behind the counter asked if I could drive a manual, to which I replied "Gladly." He handed over the keys to a 335i convertible.
I drove over early the next morning to pick up the X3. The official prognosis from the shop foreman contained no faults, deeming that the vehicle is "operating as designed," a nice little phrase that doesn't say, "Everything is working fine." The throttle delay/surge persists. We'll be following up in the coming months, doing testing of our own in hopes of finding out what's causing this wart on an otherwise splendid package.
| Our Car |
| Months/miles in service || 5/10,276 |
| Avg econ/CO2 || 19.9 mpg/0.97 lb/mi |
| Energy cons || 169 kW-hr/100 mi |
| Unresolved problems || Throttle lag |
| Maintenance cost || $0 |
| Normal-wear cost || $0 |