Completely stock engine with 74,000 miles on it stumbling between idle and 3,500 RPM
 

Recently my BRZ has begun to stumble at RPMs below about 3,500. The drivetrain is completely stock and never been modified. At first I only noticed it at throttle tip-in. However, over the last few months it has become more frequent, regardless of throttle position. In fact, this morning on the highway in 6th gear at 62 mph I floored it and it seemed to stumble two or three times per second for maybe three or four seconds. I have never seen a single CEL in this car, and the car has always been maintained impeccably well. The spark plugs have 15,000 miles on them. I always use gas from good stations that see a lot of turnover. Primarily that is Shell and Conoco.
Does anyone have any idea what might be causing this? At first it wasn't really a big deal, but it slowly seems to be happening more often in a wider variety of conditions.
Thanks!

Does it only happen on sudden(ish) throttle position change?


Have you logged at all? Even if it's not throwing a CEL, good datalogs might indicate the root cause. Especially if you can log the issue happening.


Odd as it sounds, verify the battery connections are good - clean and tight.


My first real guess is MAF sensor, possibly the idle control in the throttle body in need of a cleaning. I've had issues like this with a different car using MAP and of course that's barely similar, so these are wild guesses to get things rolling.


I had issues like this occasionally (especially from a dead stop) with my OFT tune on the '14... so it can be 100% tune related. I doubt that's your issue but note it just in case it makes someone think of something.
Hope it's an easy fix.

Edit: Is your car tuned and does this only happen when it's below 50 degrees?

Logs. Just click everything.

The tune is original. It happens in all temperatures.

Sounds exactly like a bad coil pack to me. Had these symptoms on a previous car

Oooh, good question. It does only happen when there is a sudden(ish) change in the throttle position. What does that indicate?

I'll ensure the battery terminal connections are clean and tight. I'll also clean the MAF. Those are quick, easy things to do. Thank you!

It means something is slow to react, I think. My inclination is to suspect MAF more specifically than before... time will tell.



You should see it in a log, regardless. Logs are incredibly useful. As @Ultramaroon said, log everything you can. If you don't have the tools and this isn't solved easily, I'd consider that the first thing to figure out - how to get some good datalogs.

I agree this sounds like a coil pack if everything else is stock. Even one or 2 bad ones can cause this.

Sent from my ONEPLUS A5010 using Tapatalk

I'm surprise no CEL have lit up for ignition coils (if it is the coils)

I ensured the battery terminal connections were clean and tight. I also cleaned all connections and the sensor on the MAF. I'm going to drive it for a bit and see if that solved the issue. If I don't come back to this thread within a few weeks you can expect that fixed it. That said, I expect you'll be seeing me post here again soon.
Again, thanks for all the help.

My car is modified, but I encountered an issue similar to this. I would tip in at around 3500 and it would fall on its face until 4500 rpm and clear up. I changed plugs and one bad coil pack. Didn't resolve issue. I had the car smoke tested, nothing. Swapped MAFs with a friend, nothing.

In the end it ended up being two bad direct injectors so I replaced the entire set for good measure. Resolved the issue.

Despite having a factory tune if you can even log fuel trims it would give us more information than nothing at all. Most scan tools or obd readers can do at least that. When I had my fueling issue I was one point leaner than target when I was on throttle, and at idle my fuel trims were high positives, like +14 or so.

EDIT: if it's between idle and 3500 it might very well be coil packs. Regardless logging the data mentioned will help you track the answer down.

I agree with the others, it’s probably the coil packs.

Now that’s something I haven’t said since my Audi days...

Well, the problem persists. It is happening anywhere between idle and 3,500 RPMs, regardless of the amount of throttle input. I'm hoping to have a friend log it for me sometime soon. Still no CEL. The problem seems to be getting worse, but still happens only intermittently.

Hello Pat,
Did you manage to find your problem ?
Could you tell me if your feeling with your car is comparable to this old video ?
[ame="https://www.youtube.com/watch?v=Ddl4nDEzQOM"]https://www.youtube.com/watch?v=Ddl4nDEzQOM[/ame]

Hey B.Pod, thanks for checking in with me. I did not manage to find the problem yet. That said, I haven't experienced the problem since soon after I last posted. I had a friend log it while I was driving, but I could not get the car to stumble as it had previously. I wonder if it has anything to do with the cooler temperatures here now.
Some people here think it is an issue with my coilpack(s). If that were the case, might the problem go away when ambient or intake temperatures are colder?
The video posted above is similar, or maybe the same, type of behavior I have seen in my car. That said, I see it in all gears, not just first. And not just at full throttle.

Couple things; by stumble at throttle tip in, do you mean that the car feels shuddery when just gently opening onto the throttle? Does it happen when you lift off the throttle as well?

Regarding the bolded text, does it look like this?

[ame]https://www.youtube.com/watch?v=3AU035Pvkp0[/ame]


6th gear at 62mph sounds like really low RPMs on either MT and AT gearing. If I suddenly floor it at low RPMs (sub 2.5k) my car almost "shudders" and the tachometer "jolts" around briefly but only at the initial moment of acceleration, not later on like in the video.

It is not happen just when gently opening the throttle. It can happen at any open throttle position. It never happens when closing the throttle. Only right when I open it some amount.
Yes, my car look like what happens in that video.

Check out this thread, then. http://www.ft86club.com/forums/showthread.php?t=66620

Sounds like a DI failure?

Possible. Unlikely.

Seems so minor. I wouldn't worry about it. Check all intake hose clamps and clean maf sensor.

Pat, post those logs as a baseline. They are valuable.

Do you know how to https://datazap.me/ ?

Thanks, Ultramaroon. I know nothing about logging data. @fika84 did it for me. Maybe he can chime in here.

Transient ignition retard is aggressive in the stock ECU and OFT OTS. I think throttle tip in might be able to trigger it despite enrichment, not sure though.

Good friends are cool. Or is it the other way around? ;)


It would be interesting to see if something is operating in a borderline manner. Worth a shot.

A log of fuel trims would be helpful

perhaps some bad gas that has gone ???

22R

Possible, but unlikely. It lasted for months through many tankfulls from many different gas stations.

the studering RPM under load is caused by a bad A/F sensor which directly is affecting fuel injection strategy due to abnormal signal although still within monitor threshold for ecm monitors, so no codes set , had this issue on a 14 GS350 exact same condition , disconnected A/F sensor placing vehicle in open loop fault (thus CEL is illuminated) but it goes to a default map and RPM studder went away , replaced (in this case) both A/F sensors and issue was fixed.

Yes its possible bad 02 sonsor cauld cause hesitation under load but so could a bunch of other issues like bad maf sensor dirty maf or condensation on maf, coil packs misfire dont always throw code or light CEL till certian misfire thresholds reached. Could even be knock due poor fuel or bad injectors , fuel pressure issues or di computer not earthed vaccuum or exhaust leak or dozzens of other issues.



Without reviewing logs of issue with extensive list of parameters logged everyone is just guessing.


Would be unfortunate if this guy go and buy a $200 02 sensor only to find its not the problem.

I said disconnect the Air fuel sensor for the vehicle to go into open loop fault and see whether the symptom goes away You wont have to go out and buy one to see whether the problem would be fixed its a quick check disconnect the A/F drive it , if symptoms goes away get a new one If its still there reconnect the A/F clear the code and continue diagnosing. voila! The O2 sensor is not at fault Its the A/F .

here are attached of two data files I logged of the condition. first one shows the flutter occur in the RPM parameter second picture shows the result after only disconnecting the A/F sensors in this case B1 and B2. After the result I replaced the sensors and confirmed my findings.

its worth a shot to disconnect and see whether the symptom goes away its free diagnostics lol

I've been trying to think of another fault that would be masked by forcing open-loop operation and I can't think of any.


I'm inclined to believe this is a valid test.

Yes i can see your logic.

However disconnecting the 02 sensor is may to send subaru ecu (86/brz same) into limp mode (not just open loop) where i believe it uses default maps and derives it load calculation from rpm and a default table instead of MAF sensor signal. So your not only ignoring the 02 reading your likely ignoring the maf sensor as well. And possibly other sensors, and running extremely conservative default fueling/timing maps and likely not VVT cam control and rpm limited to about 4000. Its possible that in limp mode you may also mask a problem in other areas not just the 02 sensor. this maybe different on toyota ecu logic.

It also possible that the car has developed and exhaust leak which has caused the ecu to use a lot of fuel trim to try and correct a perceived fueling issue, which in turn has cause the rough running issue.
disconnecting the 02 sensor would again mask the exhaust leak issue and the car would likely run ok .

stutter or hesitation could also be caused by poor quality fuel inducing knock and ecu pulling timing, again pulling 02 sensor and running on conservative mapping may mask the poor fuel.

unfortunately these cars also have coil pack issues which can cause misfires/hesitation under load and dont always trip the cel threshold for misfire and also Direct injector seal fails which dont always trip cel and cause hesitation stutter under load.




In your case with the V6 lexus the data on your screen shot appears to show a clue to the issue

Target AFR is 0.997 lambda


AF Lamba B1S1 = 1.2
AF Lamba B2S1 = 1.092

that seems to indicate issue on the Bank 1 afr sensor or possible exhaust leak. as the B2 sensor appears to correlate with target afr but the B1 sensor is reading very lean. assuming that data was in condition with both sensors plugged in ?

Hey Pat, did you manage to find what is going wrong on your car ?

Here is another video of hesitation I experienced on my car :
https://youtu.be/jHftQGXWPgs
What do you think about this hesitation behaviour ?
I'am not on full throttle but just trying to drive smoothly in the trafic...
The drivability is not alaways as bad as the video example but never smooth like an atmospheric engine shoud be.
No MIL, No clue...

Unfortunately I still don't have a resolution. However, I have not experienced the problem in a couple months. I don't know why that is, but it may be due to cooler ambient temperatures. I'm just waiting for it to reoccur at this point.
Your car seems to exhibit a similar, but I don't think identical, behavior. Mine isn't that consistently bad, and not to the same degree.