Originally Posted by taifei

On my 5-6 start up of the day, after about 30 minutes of driving + 30 minutes of sitting, I tried to start my car and the idle was very rough with rpms around 500. It felt like the car was on the edge of stalling. I shut it down and tried again a minute later and same results. Waited about another 5-10 minutes and it started up a little rough, rpms around 900, but didn't feel like it was going to die on me, so I let it idle for a bit and drove it home. Once I was home, I shut it down for about 30 minutes, plugged up my obd2 scanner and torque app and started logging the fuel trims which showed it fluctuating around -10 to -15 on the STFT. Long term was showing up around -10.2. I unplugged the battery, let the ecu reset, started up the car again after about 2 hours. The start was the same, slightly rougher than normal, around 900rpms. Fuel trims were still fluctuating between -10 and -15. In the morning, complete cold start, engine fired up fine, felt like normal. Idle was probably around 1300, but fuel trims still hovering around -15. By now the LTFT is showing -10.8. Driving around shows normal STFT ranging from 9 to -9 but mainly staying within 5 to -5. However, whenever I step on the clutch, the STFT starts rising back up to -15, sometimes hitting -25. Later this day, after another 40 minute drive (my 3rd or 4th drive of the day but the earlier ones were no longer than 10 minutes), and 45 minutes parked time, I tried to start the car and the low and almost stalling roughness occurred again. RPMs during idle was logged as 561, 435, 479.. (STFT was 0 but could have been that I did not give it enough time to register.) 2nd start logged rpms 155, 693, 739, 744, 779, 870, 902 in about 2 second intervals. The slow climb in rpms can explain the slightly rough starts that smooths out when it reaches normal idling revs. On my drive home, I noticed that sometimes the STFT will hit -25 and found out that if I held it at 1500 rpms in 1st gear, it will be -25, but 1700+ it will be back in the normal single digit range. Only thing I have done to the car was fill up a full tank of gas and install a catback (tanabe medalion touring). It doesn't seem like a catback should be the issue and is just a coincidence, but I guess the next step is to bolt that back on and check since that has been the only change. So far, I've checked the coils and plugs while doing a compression test. 240 235 240 250. Valved adjusted by blacktrax in april. I'm still learning the torque app so I will try to set it to log different data. Just going to shotgun the list of things to check, but if someone has a good idea of what is going on, that can save me a lot of time.