Odd set of symptoms - running strange

[Paris MkVI]

2015 Mustang GT - Yesterday the throttle started behaving oddly. Acceleration to travel speed is normal. Then, when you ease back on the throttle to maintain speed, she starts struggling, running rough and losing power. Giving her a little more throttle makes no difference. Giving her a LOT more throttle (80-100%) does. This behavior is consistent and repeatable.

While this is happening, I am getting messages after starting indicating the "Hill Hold" feature is not available. Also, once parked, the tail lights remain lit. They remain lit after I have closed the door and walk away.

She was fine yesterday morning. This all started, all at once, yesterday evening. Thoughts?

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[IPOGT]

Original battery? Disconnect and Test your battery, if good, wait 2-3 mins and reconnect and run. See if that straightens out. Weak/old batteries can do very weird things in these cars. I’ve seen it. They still start, but make the car do weird stuff. That’s the first place I’d look.

 

[SrBio]

This may sound ridiculous but check your brake fluid. I had 15 Chevy work truck that had same symptoms. It would go to reduced power, hill start assist not available, all kinds of lights on. The truck had a rear brake line leak.

 

[Paris MkVI]

OK, we all know about the chip shortage and all the issues that come with it. We know about some folks remaining on unemployment instead of going back to work. We know about crazy prices for used Mustangs and other vehicles.

It's a perfect storm at dealers. I have an appointment for three weeks from now. They are that backed up. It's pretty much that way throughout the area. If anything is transmission-related, they don't have a transmission tech - they quit, Not enough other techs, either. And parts? Some things are way back-ordered. I heard today about someone who had their F150 at the garage for 9 weeks - just waiting on parts.

I tried disconnecting the battery for 45 minutes. Unfortunately, it made no difference at all.

I know I have options other than dealer service. But I have had little-to-no success finding another shop I have confidence in where I live. Even if I did, that still won't address the parts issue.

We're at the point where we're going salvage yard shopping for five year-old cars. That is kinda sad.

 

[Mach VII]

Check sensor on brake pedal, it has a small pad that likes to fall apart and do things like you are experiencing...

 

[Cobra Jet]

Check sensor on brake pedal, it has a small pad that likes to fall apart and do things like you are experiencing...

@Paris MkVI

Yes, definitely check for the brake pedal pad issue -see here:
https://www.mustang6g.com/forums/threads/brake-light-switch-near-pedal-failure.122100/

If it's not that, then check the rear axle thrust washer, here:
https://www.mustang6g.com/forums/threads/abs-advancetrac-power-steering.162475/#post-3308430

 

[fmc_smt]

OK, we all know about the chip shortage and all the issues that come with it. We know about some folks remaining on unemployment instead of going back to work. We know about crazy prices for used Mustangs and other vehicles.

It's a perfect storm at dealers. I have an appointment for three weeks from now. They are that backed up. It's pretty much that way throughout the area. If anything is transmission-related, they don't have a transmission tech - they quit, Not enough other techs, either. And parts? Some things are way back-ordered. I heard today about someone who had their F150 at the garage for 9 weeks - just waiting on parts.

I tried disconnecting the battery for 45 minutes. Unfortunately, it made no difference at all.

I know I have options other than dealer service. But I have had little-to-no success finding another shop I have confidence in where I live. Even if I did, that still won't address the parts issue.

We're at the point where we're going salvage yard shopping for five year-old cars. That is kinda sad.

Try being the guy fixing this stuff .

 

[Paris MkVI]

If you have knowledge/experience with limp-home mode, please share. I am wondering if the behavior I've described matches that mode.

 

[Paris MkVI]

OK, today is finally appointment day, and she's at the shop. Hopefully I'll have a diagnosis soon, and then we'll see how long it will take to get the work done.

I know a guy who waited nine weeks for parts for his F150, so we'll see. . .

 

[Rapid Red]

That's life in the fast lane, maybe calling a car that has balls, her pisses it off ?

LMAO

 

[Paris MkVI]

OK, the tallight issue is that brake switch up on the pivot point of the pedal.

The odd engine behavior is one of the intake runners. Looking at a replacement.

 

[SensesFail]

OK, the tallight issue is that brake switch up on the pivot point of the pedal.

The odd engine behavior is one of the intake runners. Looking at a replacement.

Delete the IMRC and tune the rest out.

 

[Paris MkVI]

" Delete the IMRC and tune the rest out. "

I'm afraid you are going to have to decode that. I am not a mechanic/technician.

 

[SensesFail]

" Delete the IMRC and tune the rest out. "

I'm afraid you are going to have to decode that. I am not a mechanic/technician.

Sometimes the intake manifold runners get stuck (common issue, which also happened to me) that causes them to be either stuck open or closed that leads to an incorrect amount of air into the engine and confuses the computer because the amount of air isn't calibrated for. It can lead to loss of peformance, misfires, rough idle, and general drivability issues. There are kits you can purchase called IMRC Delete or IMRC Lockout (they're the same) by removing certain components on the intake manifold that cause it to get stuck in the first place. You can then have a professional tuner program your car to the now correctly adjusted amount of air coming into the now permanently open intake manifold without having to worry about the runners not working again. I've personally used Palm Beach Dyno. Have both done at the same time btw. Do not IMRC delete without having a tune ready.

 

[Paris MkVI]

Thanks for decoding - I appreciate that.

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