A tale of mystery (tuned to stock, rough idles and misfires)

[spike021]

Some of you know a bit of the history, but here's kind of a summary:

So the way it started out was like this... Several months ago (July), I had a dyno tune done with aftermarket headers (JDL UEL catted) and a (DeliciousTuning) flex fuel kit. Things worked fine for a month. Then I started having rough idle and shuddering, mostly at idle and usually once the car was warmed up. Also at that time the tuner/shop recommended running ethanol stabilizer/fuel cleaner through the system, so I did that. Didn't help the issue. After two or so times of reeeally bad misfire, flashing CEL, and almost stalling, I went back to the shop I had the tune done at (by now it's October but issues began mid-August), had the shop remove the headers, flex fuel kit, and tune. They saw a busted cat in the JDL headers, blamed that and didn't do any further troubleshooting. The FF kit was still "installed", but not plugged into the car; only the fuel line going through the sensor was still connected, but no signal or anything was going to the car from the kit (so basically just a fuel line extension of sorts).

Between October and this past week, the car mostly drove fine but at idle there would be times where the revs would surge on their own causing a light shudder through the car that I didn't remember before having the tune done originally. Like, noticeable enough where it very much so felt "off" to me and I knew something wasn't quite right. However, with no obvious misfiring or CEL/codes, I figured I should wait it out a bit longer just in case I was overreacting.

Note: I can't seem to "feel" this roughness while actually driving. For instance, I've intentionally gone on the highway and stayed at certain speeds with constant RPM to see if it would stay smooth, and it was fine.

i.e.

* 50mph in 4th gear at like 3000rpm
* 65mph or so in 6th gear at 3000rpm
* and so on...

So from my experience it only really happens:

1. at a stop and waiting for the light to change
2. occasionally as I'm slowing to a stop in neutral/clutch-in (this only mostly happened when it was actual misfires though, not just the more subtle idle issue I'm currently having)

This week things changed. One night after work I got suuuper bad misfires and CEL like the earlier time last year. I decided it would not be safe to drive and chose to tow the car to a dealer (the one I bought it from and that had done decent service for me in the past).

They basically just disconnected the battery, reconnected, did a leakdown test, and disconnected the FF kit fuel line and reconnected just the OEM line. Boom, "smooth" test drive and they handed it back yesterday.

Note: they found a kink in the DT fuel line that I had never noticed. I'll just give a few theories:

1. fuel line was kinked from the start and somehow neither I nor the shop doing the install/tune never noticed (odd since kit was bought new)
2. it happened on its own sometime in the past few months
3. tech at dealer did it intentionally or accidentally this past week, but as a way to basically put blame for these issues on the "unknown aftermarket piece" (I don't want to believe this was the case but since it was a rather obvious kink I can't believe I didn't notice it more recently on my own)

However, today the idle roughness and surging came back, and since it was happening before the most recent misfire/CEL situation, I'm super worried the issue isn't really fixed.

Also, the first time I got the CEL a few months ago, the only code was P0303 (until the end when it got to the worst point and then multiple cylinder codes), this time it was P0302.

Supposedly the dealer checked spark plugs and whatnot. The first shop also checked spark plugs, and yet another shop a few months ago also double-checked spark plugs, coil packs, etc. for me because I felt it necessary to get a second opinion.

I _think_ at this point it's safe to rule out those electrical bits, but who knows.

I'm not a mechanical person. As much as I love driving this car and even enjoy most of its crickety quirks, I'm not someone who wrenches on cars. All I can do is think of random theories and check in with other people to see what they think.

When I called in to the dealer today and spoke to the service manager about the idle issue happening, he looked for relevant TSB's and saw this one: 11-193-19

Link to TSB: https://static.nhtsa.gov/odi/tsbs/20...68604-0001.pdf

However, he was wrong as this TSB appears to only affect AT BRZ's.

At this point I'm really struggling. I don't regret doing the tune and having the flex fuel kit + headers; they were super enjoyable.

But it is my daily and really it's my baby (first car). I can't bear to drive it knowing it might not be entirely healthy. So I'm posting this to get a wider discussion going and see if anyone might have any ideas.

Tonight I also was able to use Ecutek Connect and the iOS app to do some datalogging.

Here's one datalog (about 8 minutes of pure idling) with about two different moments where the strange rough idle occurred:

https://datazap.me/u/spike021/log-1580534456

If anybody has any advice I'd really appreciate it!

Thank you!

[Ultramaroon]

Hey, Spike, can you take another log recording all the params. Need stuff like engine speed and throttle opening while it's doing its weirdness.

[spike021]

Originally Posted by Ultramaroon

Hey, Spike, can you take another log recording all the params. Need stuff like engine speed and throttle opening while it's doing its weirdness.

Ahhh fair enough. I'll probably go back out in the morning for more logs.