Hey all-

Not sure if this should be here or in "Tech", so apologies in advance if it's in the wrong place.

Recently bought a new-to-me 05 X with 70K. From the test drive up to a day or so ago, the car impressed with it's ability to shove me back in the seat from almost any speed in any gear.

Now however, the snappiness and "edge" of the motor seems lost or dulled.

1st thing I noticed was that from a stop, first gear/half throttle starts are attenuated rather disappointingly with a premature dump right up to second gear. I *swear* it would hold first longer just a couple of days ago. On the highway, which is 95% of my driving, it seems slower than it was to both downshift and then pick up passing speed, a task it impressed me with previously.

2nd thing is that while the engine revs up freely, it just feels like there's no torque. My foot is in it, it's revving and making noise, but it just feels kinda soft.

Now, here's where I get to the big dope part. The other day when I stopped for gas, I grabbed the 87 out of force of habit. However, I only put about a quarter tank in. I didn't think anything of it at the time, but these issues became noticeable shortly afterwards; I only realized it after reading through the forums. (Prior to this particular brain-fart, I have always put in premium.)

Yesterday evening, I was down to maybe an eighth of a tank so I filled up with 93 again. Drove to work this morning (40 miles or so) and it seemed about the same, maybe slightly improved, (I think I want it to feel improved more than an actual improvement) but it's still definitely not feeling like the same sleeper sedan it did a few days ago.

No lights on the dash, no other change in the way it starts or stops. The car is unmodified.

I have spent what time I could scouring the boards here and going through the FAQs (thank you all) for potential solutions and indicators as to what might be the problem aside from potentially a retarded timing issue resulting from detonation caused by the lower octane fuel. If that is the case, man is that a noticeable difference.

Should I wait it out and see how it is as the fresh tank of 93 works its way back through the system? Would the presence of lingering 87 continue to be a problem?

Then also, why the seemingly sudden change in the behavior of the trans? It just feels like it's making the 1-2 shift way too soon, before it can really build any sort of power in 1st. Time to reset the ECU? Or perhaps has all the highway drudgery "taught" it to behave like grandma's car?

Thanks for the sympathy, help, support, noob mocking etc.

 

Sounds like your cars ECU has relearned itself with your lethargic highway habits. And since you drive almost all highway, I'm not surprised. Another answer would be that maybe your ECU was reset prior to this experience. But that would be much too noticable to be an accident. As for your brain fart, I would empty the tank as much as I can before the next fill up. You can always reset your ECU and drive like a mad man for a week so that the car can relearn to feel aggressive.

 

Like silver9 said the ecu and transmission learn your driving habits. They will soften up or harden up given enough consistency. And with the 87 octane it pulled timing for sure. The ecu is quick to pull it, but slow to advance it after wards.