A little while ago, my vehicle started throwing a few emissions codes, starting with P0455, then P0449. I replaced the Purge Valve and Vent Valve solenoids, and got rid of that issue entirely. However, right after I got the new vent valve solenoid on the vehicle and verified that code was resolved, it began giving me the P0175 and P0172 consistently.
LT fuel trim sits at -19.5 for both banks at idle, which seems to be its floor, and only ever reaches 0 at WOT, but never above 0. Even warm, it stays at -19.5. ST fuel trim starts each trip around -5, but slowly creeps into the -10 and lower range as the drive goes on. Once warmed up, it seems to bounce anywhere from -14 to -5 at idle. It does increase with the throttle, but then adjusts itself to remain rich. It can’t seem to reach that equilibrium. It also hesitates slightly on the first start after a few hours sitting, but runs fine after about 5-10 seconds.
I recently drove through the West Virginia mountains with a heavier trailer behind my Tahoe, and when it kicked down into 2nd gear to take a hill at 65 MPH, 4,000ish RPM, you could hear a whistling sound from the front of the vehicle under heavy load, which took a couple seconds in 2nd gear before it started and ended as soon as it shifted back into 3rd at the crest. I had replaced the purge valve a couple of days before the trip as well.
Would I be chasing a vacuum leak at this point, or could it be something else? The MAF reads .7-.8 lb/Min at idle, with a MAP of around 9.4 inHg, which both appear to be around normal. My next step is to try cleaning the MAF since I did add a CAI about 9 months ago, but I would’ve thought that would create issues before the 14k mile mark on the tube and filter. I replaced the filter, but had no luck on the trims readjusting.
I’m brand new to Maryland and want to make sure she passes emissions testing without any real headaches. Never had to deal with them before, so it’s a new world of worry.
LT fuel trim sits at -19.5 for both banks at idle, which seems to be its floor, and only ever reaches 0 at WOT, but never above 0. Even warm, it stays at -19.5. ST fuel trim starts each trip around -5, but slowly creeps into the -10 and lower range as the drive goes on. Once warmed up, it seems to bounce anywhere from -14 to -5 at idle. It does increase with the throttle, but then adjusts itself to remain rich. It can’t seem to reach that equilibrium. It also hesitates slightly on the first start after a few hours sitting, but runs fine after about 5-10 seconds.
I recently drove through the West Virginia mountains with a heavier trailer behind my Tahoe, and when it kicked down into 2nd gear to take a hill at 65 MPH, 4,000ish RPM, you could hear a whistling sound from the front of the vehicle under heavy load, which took a couple seconds in 2nd gear before it started and ended as soon as it shifted back into 3rd at the crest. I had replaced the purge valve a couple of days before the trip as well.
Would I be chasing a vacuum leak at this point, or could it be something else? The MAF reads .7-.8 lb/Min at idle, with a MAP of around 9.4 inHg, which both appear to be around normal. My next step is to try cleaning the MAF since I did add a CAI about 9 months ago, but I would’ve thought that would create issues before the 14k mile mark on the tube and filter. I replaced the filter, but had no luck on the trims readjusting.
I’m brand new to Maryland and want to make sure she passes emissions testing without any real headaches. Never had to deal with them before, so it’s a new world of worry.
