Chasing a rough idle

I've had a slightly rough idle for a while now, no codes or rpm fluctuation, but it sounds and feels like a small sputter/pop every few seconds, only when fully warmed up. 2010 with 62k miles, injectors and valves recently cleaned. Logged HPFP pressure after turning the car off and pressure only rose to 1400 so I replaced relief valve (autotech internals btw). Afterwards, I did the same test after a drive and pressure only reached 950, but then the next day reached 1700. My HPFP pressure has never looked bad in logs or cruising around, except for occasionally dipping into the 390s for a split second at idle before going back up to around 415. Also, pressure is always around 250 on decel, but not sure if that's normal or not. Either way the rough idle was still there so I cleaned and rebuilt the HPFP with the CS kit. Now the idle is slightly worse and LTFT is consistently around -10, -11 at idle and no change to HPFP pressure. The car drives perfectly fine when not idling and fuel trims even out. I've also checked for vacuum leaks a number of times. Any advice on what to check next?

 

Fuel pressure seems fine. Your PRV was fine, as long as you don't see pressure abruptly start dropping off. That would indicate the valve opening. You're limited to how much the pressure is going to rise based off heat in the engine bay. Last time I did it, it only reached ~1430 before starting to slowly drop off.

If you could throw up a log of idle that'd make things easier to tell if something is off.

 

Gotcha, here is a long idle log, let me know if I should be logging anything else

 

After posting the last log, I found a loose vacuum line and idle improved only slightly. LTFT is still usually around -10 at idle but after some more research it sounds like that isn't such a big deal, but I'll still include a new idle log just in case. As for the sputtering idle maybe I still have a slight vacuum leak somewhere? I've noticed sometimes during light throttle my AFRs will go to around 15.5 for a second. I've hooked up my ghetto-DIY smoke tester to the intake manifold and the intake but found no leaks. Thanks for your reply btw, this newbie section is definitely for me lol

 

Log looks fine. Everything is pretty consistent and the STFT never moves so I don't see why it might be sputtering. Is there a custom tune on the car that was done before the cleaning the injectors and valves?

Also just the heck of it you can always clean the MAF sensor.

 

Yes actually, PD tuned me before the injectors were cleaned, I got some advice elsewhere that I shouldn't need a revision or anything and the sputtering was already there before injector cleaning. Still might send Will a message/log but just wanna make sure everything is mechanically sound first. MAF sensor was just recently cleaned too

 

That's probably why your LTFTs are high. Not a big deal, just something to note.

Considering you're not getting a misfire code I don't think it's anything spark plug/coil related. You could try unplugging the EGR valve if you haven't deleted it and see if that changes anything. That can cause weird idle issues and cleaning it and the tube between the valve and the intake manifold would be a good idea if you haven't done it yet.

 

EGR is deleted but yeah after the injectors were cleaned LTFT was -7 at idle. It was when I cleaned the HPFP and replaced the relief valve that it went to -11. The car does feel happier in lower rpms now and its good to know I shouldn't be worried about the LTFT, but still chasing the weird idle. Maybe an issue with vvt or pcv valve?

 

Your primary o2 sensor might be something to look at

 

Good call, I just looked and noticed the 02 sensor wire isn't routed through the normal spot but instead sits on the turbos heat sheild... gonna fix that and look at the sensor

 

pulled both o2 sensors and they are super gross. know of any good replacements? the OEM ones are pretty pricey

 

I had luck running "Automotive-Leader" brand chinese-but-really-just-bosch O2 sensors to replace the NTK sensor that came with my AEM wideband. It's lasted nearly 40k miles and still reads true.

 

Ntk is the way to go apparently. I don’t think I’ve seen anyone else have great luck with many other brands

 

Not trying to highjack the thread but have you noticed any KR during WOT? I’m chasing this exact idle issue with no real mechanical sign to follow. My ltft an stft aren’t bad but just trying to see if maybe an 02 could be my issue during WOT