2015 BRZ - Rough idle + acceleration struggles - Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community

Jfheisenberg · 11-16-2020, 06:07 PM

Hi All - Cant figure out whats going on with my car, so here i am.

The car: 2015 brz 54k miles, full exhaust/tuned with OTF stage 2+ and perrin cold air intake. Spark plugs were changed 4 months ago. Never had this kind of problems with the car and all maintenance is done on time. Always use 93 octane and try to go to the same Shell gas station

The problem: Few days ago, i started to notice that the car idles rough. Normally, the car idles at 800 rpms and are steady. Now, the rpms drops to about 600~ rpms and car kind of wants to halt but doesn't, then the rpms come back to 800 again. Also, when accelerating on 1st and 2nd gear i can feel that the car is struggling to run throughout the rpm band.

These are the only to symptoms as there is no CEL code. Today, i cleaned the throttle body (not that it was that dirty) to see if it make a difference, but nothing.

I definitely feel that something is off with the car. Any ideas?

Lantanafrs2 · 11-16-2020, 10:03 PM

Which plugs did you use? Put some air in your tires

gen3v8 · 11-16-2020, 11:15 PM

That Air Fuel Ratio and timing going up and down is not right. whatever is causing that is the problem. An air leak or fuel pressure maybe, dirty air flow sensor even reload the tune.

Gloonge · 11-16-2020, 11:39 PM

The afr swinging at idle is your issue. I would clean the maf and see if you can get your hands on one and swap it.

Also check your air filter.

humfrz · 11-17-2020, 12:38 AM

You might consider getting a new MAF -

Jfheisenberg · 11-17-2020, 01:58 PM

Quote:

Originally Posted by gen3v8

That Air Fuel Ratio and timing going up and down is not right. whatever is causing that is the problem. An air leak or fuel pressure maybe, dirty air flow sensor even reload the tune.

Quote:

Originally Posted by Gloonge

The afr swinging at idle is your issue. I would clean the maf and see if you can get your hands on one and swap it.

Also check your air filter.

Quote:

Originally Posted by humfrz

You might consider getting a new MAF -

Thanks for the advise. I just clean the MAF sensor, it was a bit dirty but not much IMO. Put it back in and its still the same (same numbers on the OTF live stats). The air filter was changed on June. At this point im just going to the shop i usually go for diagnostic.

Uncle86 · 11-20-2020, 08:11 PM

o2 sensor? Or a small exhuast leak? I had the acceleration issues without a cel and found a leak at one of the header gaskets, but that was my issue.

Sent from my Pixel 5 using Tapatalk

Jfheisenberg · 11-21-2020, 05:04 PM

Yesterday, i went to the shop where i get all my stuff done to the car. The tech mentioned that there is some air leak, so suggested to swap my perrin throttle body inlet to the OEM one. So i did that, and still having the same issues. We also replace the clamps and to my eye, everything looks correct. Also, i tried to one of my friend's inlet hose that he runs in his FRS and issue is still there.

Next, i flashed back to stock with the OTF and then reflash to stage2+. Unfortunately, problem is still there.

I was thinking maybe the gas was bad? So i needed to refill and went to shell and got vpower 93 octane. Sadly, this was not it neither. Car still idles rough and sluggish acceleration is more pronounce on lower gears from 1k rpm - 3.5rpm. After passing 4k rpm the issue is not felt.

No idea what the problem can be as there is no check engine light.

My next step will be to remove the perring CAI and put back the stock air box. However, if the issue was with the air filter, wouldn't the maf sensor throw a code?

Jfheisenberg · 01-04-2021, 03:40 PM

Car is still having the same issue. Cant seem to figure out what the problem is.

About 1 month ago, i remove my bumper and noticed that the CAI filter has come off (I thought this was the problem), so then i remove the CAI entirely and put the stock box and new filter back on. This didnt fix the problem.

I have taken the car to the shop and, they dont see any leaks. Shop refer me to go to Subaru dealer to have my ECU check. I went to Subaru dealer, they see nothing wrong with the ECU, and since im catless, they refer me to a Tuner shop (which i dont have one close to me)

Also, attempted refreshing ECU with OTF again, but didnt help. No CEL codes, but problem still there.

Any one has any advise on where i can look next?

BigTuna · 01-04-2021, 04:16 PM

Is your air conditioning/defogger on?

Jfheisenberg · 01-04-2021, 04:51 PM

Quote:

Originally Posted by BigTuna

Is your air conditioning/defogger on?

No

whataboutbob · 01-04-2021, 08:39 PM

Any check engine lights? Can you use a scanner to see if there any past/pending codes?

FR-S2GT86 · 01-05-2021, 12:14 AM

I think you're going to have to start posting some data logs for some of the guys on here to see in order to help you out.

Thefalls · 01-05-2021, 03:34 PM

Did you have a look at your throttle body if its stuck open?

Normally you should have had CEL.

11-16-2020, 06:07 PM	#1
Jfheisenberg Senior Member Join Date: Jan 2015 Drives: 2015 BRZ Series Blue WRB Location: North Jersey Posts: 830 Thanks: 371 Thanked 204 Times in 156 Posts Mentioned: 2 Post(s) Tagged: 1 Thread(s)	2015 BRZ - Rough idle + acceleration struggles Hi All - Cant figure out whats going on with my car, so here i am. The car: 2015 brz 54k miles, full exhaust/tuned with OTF stage 2+ and perrin cold air intake. Spark plugs were changed 4 months ago. Never had this kind of problems with the car and all maintenance is done on time. Always use 93 octane and try to go to the same Shell gas station The problem: Few days ago, i started to notice that the car idles rough. Normally, the car idles at 800 rpms and are steady. Now, the rpms drops to about 600~ rpms and car kind of wants to halt but doesn't, then the rpms come back to 800 again. Also, when accelerating on 1st and 2nd gear i can feel that the car is struggling to run throughout the rpm band. These are the only to symptoms as there is no CEL code. Today, i cleaned the throttle body (not that it was that dirty) to see if it make a difference, but nothing. I definitely feel that something is off with the car. Any ideas? Last edited by Jfheisenberg; 01-12-2021 at 07:32 PM.

01-04-2021, 04:16 PM	#10
BigTuna Senior Member Join Date: Jun 2015 Drives: 2013 WRB BRZ Location: Ohio Posts: 672 Thanks: 258 Thanked 477 Times in 275 Posts Mentioned: 4 Post(s) Tagged: 0 Thread(s)	Is your air conditioning/defogger on? __________________ 2013 WRB "Build" Thread

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11-16-2020, 10:03 PM	#2
Lantanafrs2 Senior Member Join Date: Jan 2018 Drives: 2013 frs red Location: South Florida Posts: 3,570 Thanks: 2,579 Thanked 3,132 Times in 1,684 Posts Mentioned: 6 Post(s) Tagged: 1 Thread(s)	Which plugs did you use? Put some air in your tires

11-16-2020, 11:15 PM	#3
gen3v8 30 minute maintenance Join Date: Oct 2020 Drives: My18 wrxsti Location: Botany Bay Posts: 1,178 Thanks: 769 Thanked 1,236 Times in 631 Posts Mentioned: 7 Post(s) Tagged: 0 Thread(s)	That Air Fuel Ratio and timing going up and down is not right. whatever is causing that is the problem. An air leak or fuel pressure maybe, dirty air flow sensor even reload the tune.

11-16-2020, 11:39 PM	#4
Gloonge Senior Member Join Date: May 2016 Drives: 2013 frs raven Location: W.P.B - Florida Posts: 224 Thanks: 5 Thanked 54 Times in 40 Posts Mentioned: 1 Post(s) Tagged: 0 Thread(s)	The afr swinging at idle is your issue. I would clean the maf and see if you can get your hands on one and swap it. Also check your air filter.

11-17-2020, 12:38 AM	#5
humfrz Senior Member Join Date: May 2013 Drives: 2013 FR-S, white, MT Location: Puyallup, WA Posts: 30,432 Thanks: 29,826 Thanked 32,845 Times in 16,844 Posts Mentioned: 715 Post(s) Tagged: 2 Thread(s)	You might consider getting a new MAF -

11-20-2020, 08:11 PM	#7
Uncle86 Member Join Date: Apr 2020 Drives: 2013 Fr-s Location: SF Bay Area Posts: 56 Thanks: 0 Thanked 13 Times in 10 Posts Mentioned: 0 Post(s) Tagged: 0 Thread(s)	o2 sensor? Or a small exhuast leak? I had the acceleration issues without a cel and found a leak at one of the header gaskets, but that was my issue. Sent from my Pixel 5 using Tapatalk

11-21-2020, 05:04 PM	#8
Jfheisenberg Senior Member Join Date: Jan 2015 Drives: 2015 BRZ Series Blue WRB Location: North Jersey Posts: 830 Thanks: 371 Thanked 204 Times in 156 Posts Mentioned: 2 Post(s) Tagged: 1 Thread(s)	Yesterday, i went to the shop where i get all my stuff done to the car. The tech mentioned that there is some air leak, so suggested to swap my perrin throttle body inlet to the OEM one. So i did that, and still having the same issues. We also replace the clamps and to my eye, everything looks correct. Also, i tried to one of my friend's inlet hose that he runs in his FRS and issue is still there. Next, i flashed back to stock with the OTF and then reflash to stage2+. Unfortunately, problem is still there. I was thinking maybe the gas was bad? So i needed to refill and went to shell and got vpower 93 octane. Sadly, this was not it neither. Car still idles rough and sluggish acceleration is more pronounce on lower gears from 1k rpm - 3.5rpm. After passing 4k rpm the issue is not felt. No idea what the problem can be as there is no check engine light. My next step will be to remove the perring CAI and put back the stock air box. However, if the issue was with the air filter, wouldn't the maf sensor throw a code?

01-04-2021, 03:40 PM	#9
Jfheisenberg Senior Member Join Date: Jan 2015 Drives: 2015 BRZ Series Blue WRB Location: North Jersey Posts: 830 Thanks: 371 Thanked 204 Times in 156 Posts Mentioned: 2 Post(s) Tagged: 1 Thread(s)	Car is still having the same issue. Cant seem to figure out what the problem is. About 1 month ago, i remove my bumper and noticed that the CAI filter has come off (I thought this was the problem), so then i remove the CAI entirely and put the stock box and new filter back on. This didnt fix the problem. I have taken the car to the shop and, they dont see any leaks. Shop refer me to go to Subaru dealer to have my ECU check. I went to Subaru dealer, they see nothing wrong with the ECU, and since im catless, they refer me to a Tuner shop (which i dont have one close to me) Also, attempted refreshing ECU with OTF again, but didnt help. No CEL codes, but problem still there. Any one has any advise on where i can look next?

01-05-2021, 03:34 PM	#14
Thefalls Senior Member Join Date: Feb 2014 Drives: Corolla GT Location: Sunny place. Posts: 208 Thanks: 372 Thanked 118 Times in 90 Posts Mentioned: 6 Post(s) Tagged: 2 Thread(s)	Did you have a look at your throttle body if its stuck open? Normally you should have had CEL.

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