Engine over revs randomly w/ no throttle response
 

Hey guys & gals. About 2 months ago my car started having some random issues. First off, it would have trouble cranking, push the start button and it would flash lights and make cranking noises, but ultimately not turnover. It would do this 2-5 times then crank like normal, no issues while driving and the issue is very random (1 to 2 times a week). Thinking it might be a battery issue, I changed it. Did not make a difference.

That issue is rarely happening now, but now the car is having an issue where while driving, the car will over rev, revs itself to 7000+ RPMs with no response from the gas pedal at all. It will over rev like this anywhere from 5-20 seconds. A few times, i've pulled over, turned the car off, waited a few moments, cranked it back up and it was still over revving. This happens normally while driving the car longer than 15 minutes, but hard to say on longer drives because it doesn't seem to push the car past 55 mph. Driving in town though, when the issue comes up i have to put the car in 4th or 5th gear and ride my brakes until I can pull over somewhere.

The car is throwing no engine codes at all, and is currently at the 3rd shop hoping for something. Nobody can seem to find a cause. Current shop believes it may be an issue with the Tune, but I don't have any info whether the car has one or not, but I'm assuming it does.

It's a 2017 Subaru BRZ that I purchased April 2019 from a Subaru dealership. The list of mods from the dealer:

• SBD 500x turbo
• ark grip exhaust
• Act HD street clutch
• white line transmission bushing

I have put nearly 40k miles on the car and have not had any previous issues.

Anyone see something like this and maybe point me in the right direction?

Edit: There has been one incident of the car turning off completely while at a red light, and then not cranking for ~10 minutes, then cranking and driving completely fine right after.

Sounds like the clutch is slipping if it happens while driving. If it does it when you first start the car, it should be something in the throttle body I suppose

If you're "unsure" about the tune, get a tune for it. I wouldn't drive the car until you have this resolved

Do you notice more revs going up hill and going fast? If that is the problem it sounds like a slipping clutch.


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The driving speed doesn't seem to have an effect on this, i just noticed that when the issue is happening, it doesn't push the car over 65ish mph, so driving 70 mph+ on highway, i'm not sure that it's ever happened.

I didn't think of transmission as an issue. Also, I have not driven the car in almost 3 weeks, outside of bringing it to and from multiple shops for a looking over.

If your RPM’s go up without changing car speed then your clutch is slipping. Probably a good thing because 7K in 4th is 90ish, 5th is 120ish.

Now onto why the engine is running away, Lots of items need to be checked and quit driving it like that before it hurts you or someone else or just destroys the car. If you have a turbo then yes you have a tune. If you do not know who or how they tuned it find a local shop or buy a remote tune from Counter Space Garage. They may be able to see issues with it in the idle logs. If not you may have to log and get it to act up then they should be able to narrow down the issue.

Also check main power and ground connections. That is probably you start issue.

Sounds to me like there is a problem with the drive-by-wire circuitry. When the RPM's skyrocket, if you push the clutch in, does it disengage the transmission and continue to rev real high?

You're turbocharged so you definitely have an aftermarket tune. It would be nice to know which tuning suite was used. Have you tried pulling the cruise control stalk back with cruise control off for a few seconds to see if your tachometer jumps to 1000, 2000, 3000, or 4000 RPM in order to check if it may have been tuned with EcuTek?

I don't think it's a slipping clutch since most people would say right away if they're getting a burning clutch smell from underneath (and sometimes inside) the car.

Maybe I said this in a confusing way, but the speed does go up, it goes to 7k RPMs if the car is put into neutral, which is why I said i usually put in 4th or 5th gear, because the overrevving does not seem to carry the car over 60-65 mph.

I also have not driven it in nearly a month outside of bringing it to new shops.

Did not know this was a thing, will have the current shop give this a try

There is actually a burning kind of smell when it happens, but I'm too noob to identify the type of smell. I couldn't tell if it was just the smell from the engine revving so much or from me riding the brakes when it would happen. I did initially take it to a transmission shop, because a friend also suggested transmission but the shop said they couldn't find an issue, but I doubt they tried very hard.

To rule out the clutch slipping, as soon as the problem happens, you need to immediately push in your clutch, let off the accelerator, and shift to neutral. If your engine still revs up by itself, it is NOT your clutch slipping, it's something else. Which means you're going to have to get it back out on the road, hopefully with nobody else around and try to recreate the conditions of the problem.

And remember, you can always shut the engine off and coast to a stop in an emergency if you need to. Use your emergency brake also if you need to, that's what it's there for.

As for the cruise control stalk test to see if your tune was through EcuTek, (and you can easily perform this quick check yourself) just because your tachometer doesn't jump to one of the aforementioned values, doesn't necessarily mean that the tune wasn't through EcuTek. It could still be, but just not have the multiple maps option programmed into it. If the test fails to confirm your tune was EcuTek-based, you'll have to find a tuner or an experienced friend with tuning capabilities to help you out.

Looking at the dealer locator in the ECU Connect app on my iPhone, there is one EcuTek dealer near New Orleans, Corr Performance Tuning. Not sure where in Louisiana you are but there are other EcuTek dealers in Texas, Tennessee and Georgia as well.

I am in Baton Rouge, about an hour from New Orleans, and the shop I currently have the car with has a guy who can test the tune supposedly, but he won't be in until next weekend.

In regard to your other comment, whenever the issue arrises, if I shift to neutral, and depress the clutch the car will still over rev and will do so all the way to 7000+ rpms and in one instance was red lining, I was in traffic at the time, so couldn't coast anywhere, and just suffered through it until traffic started moving again.

I appreciate all your insights, I am hoping the guys who have the car now can help.

For the time being, unplug the throttle body and blow out the connections, who knows.

I have a spare throttle body you can swap out if that's helpful. It's likely something with the pedal input or the throttle body. Unless the pedal input map in ECUtek somehow was made goofy (0% throttle being mapped to a high percentage?)

Yeah, that eliminates the clutch or transmission as the SOURCE OF the problem. (You may still be getting slipping due to the main issue which can cause that burning smell.) Time to focus on the engine. Specifically the sensors, connectors, wires, hoses, electronic components and possibly, (but more unlikely due to the fact that you've had your car for so long and have driven it for so many miles now) the tune itself.

Update:
Original owner installed turbo manifold lower than suggested, and wrapped it. Apparently you aren't supposed to wrap it (according to SBD team). Manifold was sitting up against chassis at some point, and over time has worn a small hole into the turbo manifold. This is causing computer to improperly regulate fuel supply.

Ordering new turbo Manifold from SBD, rep said this is a common installation error.