disconnected battery, power temporarily restored?

[Brian41]

I recently posted about my 2015 sport losing power and the dealer looked at it and said they found nothing wrong and said it must have been bad fuel. Several tanks of 93 octane later, the vehicle struggles at WOT and it now hesitates, it basically lost it's "punch". A friend suggested disconnecting the battery for an hour, which I did.

The car drove great after that and all power seemed restored. However, later in the day it started getting very noticeably sluggish all over again. I have checked all hoses that I can see and nothing looks loose. There is still no check engine light. The air filter looks fine.

I know i'm not imaging this, as I had another friend who has a sport drive it and he noticed the lack of power right away at wide open throttle. My sport would normally cause torque steer at full throttle and that is now gone, it feels a good bit of torque has vanished.

I just bought it 2 weeks ago with 39,000 miles on it and the dealer where it was originally purchased said the only maintenance history they had was a oil change at 4,000 miles. It drove great the first two days and now I have an appointment this upcoming Monday at the dealer again. I'm no car expert, but could this be a spark plug issue due to the car also hesitating, but is only intermittent.

I'm getting desperate now as I feel I may have to sell this car. Does anyone have any suggestions? Anything I should ask them to check? I'm afraid there going to just say it has no warning lights and unless the mechanic driving it is very used to driving a sport, he'll probably think the car is normal. Thanks for any help in advance.

 

[Sixonemale]

I'm purely guessing and not at all an expert on this topic, but it sounds like you may have a malfunctioning PCM/ECU. I would explain to the dealer what you did, disconnected the battery for an hour and then it ran well for awhile, but then drove sluggish again later in the day. What makes this difficult is that no check engine light is coming on or any code being thrown. Perhaps someone on this forum has had the experience of a malfunctioning PCM/ECU and can chime in as to whether or not this is a potential source of your problem.

 

[thefranchise713]

Sounds like it's running fine until it learns, and so the default parameters are better than the ones that are used by the PCM for normal operation.

I'm going to guess something is offering bad data to the PCM like a MAF or something.

 

[Sixonemale]

Sounds like it's running fine until it learns, and so the default parameters are better than the ones that are used by the PCM for normal operation.

I'm going to guess something is offering bad data to the PCM like a MAF or something.

I had those thoughts also, but it seems like if something was offering the PCM bad data, especially a sensor, that a code would be thrown, put perhaps not with a bad MAF, etc.

 

[thefranchise713]

Spitballing. I feel like I've read of this situation before too (maybe not this forum) and the MAF was the issue.

Keep in mind that bad data may not always trigger a code for plausibility faults or out of range issues.