Ours does the same thing but in D. Sometimes he gets confused about which gear to be in when slow-rolling, and can't decide between staying in 2 or going back to 1, so he goes 2, rev, 1, 2, really quickly. Also happens when slowing down and going over a speedbump or into a driveway. We try to either keep him rolling and accelerate slowly which keeps him in 2, or come to a total stop which puts him back in 1. If slow-rolling and you try to accelerate too much, he stutters 2-1-2...
That behavior is normal and a result of engineering oversight or compromise; 5MPH is the exact point where it will shift between 1-2 in stop and go traffic. I run mine in manual mode (1st gear for < 8mph, 2nd gear above that) to prevent that effect, and leave space in front of me so I can go 10+MPH more often. If someone zips in front of me, fine - they needed to get over anyway and probably would have done so more dangerously later on.
This same gear-selection behavior causes a jerking near-stall when going up a steep parking ramp or hill you approach at 8MPH. At that speed, 2nd gear doesn't have the torque to conquer, so unless you get a faster approach, it'll almost-stall and revert to 1st gear with a humiliating surge. Estimate that going up any hill you'll need 2000+ RPMs and set the gear before you get there.
All of this is evidence that the transmission is manual at its core. Automatic mode is not smart enough to handle the low-speed, low-RPM range.
A few times when first using the car in the morning (always in manual) I will make the first call for a shift to 2nd. It won't make the shift, but go to a neutral spot and the RPM will drop to idle speed. Then it will re-engage 1st, and because 2nd had previously been called-for, and then shift to 2nd. Once that episode has passed, everything is thereafter normal. Yup, this started recently but sometime after 2.0.
I took the car in this morning, wondering if I was getting into clutch problems. I explained the failure to go to 2nd to the service manager, and she had the tech come in. He said something that surprised both the SM and me - he had recently discovered by accident that an '09 would not accept a manual 2nd gear command below 11 MPH. This something that does not appear in the owners' information nor in the dealers' tech info. It looks like my '08/2.0 now has the situation, though there was no information distributed with the 2.0 update that it would be so. I've experimented with it a bit on the way home, and sure enough, if I start off in manual 1st and select 2nd at about 5 MPH I can practically red-line it and no shift. It will shift if manually selected a second time above the 11-or-so. I probably get into the situation because I short-shift in my neighborhood to make sure I don't speed (as V.P. of the H.O.A. I always have to be a "good-guy"). And thinking about what I have been doing, I think my feeling that the engine was stumbling in a neutral spot was just my subconscious throttle lifting before shifting, but even that wasn't coaxing the transmission into 2nd.
Aside: While the tech was checking the transmission out on the road, he brought along the dealer's electronic fuel consumption data logger (liters per 100 km). In 15 miles of combined fast interstate, city boulevard, and congested cross streets he pulled a 47.8 MPG overall. I'll take it!
... I've experimented with it a bit on the way home, and sure enough, if I start off in manual 1st and select 2nd at about 5 MPH I can practically red-line it and no shift. It will shift if manually selected a second time above the 11-or-so. ...
Quote:
Originally Posted by trekguy
Me thinks the transmission is delaying the first shift when cold to have the engine and catalytic converter heat up rapidly to reduce emissions.
My MB SL320 did this also.
The above experimentation was done with a hot engine and transmission.
N.B. the tech didn't say that this is a characteristic of a '09 or a '08/2.0; he just noted it while working with a customer's '09.
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