I have a 2007 Pontiac Grand Prix with a NA 3800. A while back(like maybe a year ago now), I was sitting in a parking lot at my job and the car started to not want to idle properly, it would act like it was about to stall out, then rev to maybe 1.1 or 1.2k RPM's before evening back out. It would do it like every few minutes. At the time, the car had been running for a handful of hours, like 2 or 3 hours at that point. At that point in time, I didn't have my laptop with me so I never was able to run any diagnostics on the car. But recently, after I got done door-dashing(I had my laptop with me reading the PCM the entire time), and got something to eat, when I started to leave from the fast food restaurant, I noticed the car not wanting to run right, looked at the LTFT and it was sitting between -15 and -25. To my knowledge, and from what I had looked up, with it in the negative, it is trying to run rich, but the PCM is trying to combat it. Either way, I know the number is not supposed to be any bigger than +/- 10.
The car currently has 182k miles. Since 160k, I had replaced the spark plugs, spark plug wires, the Ignition Control Module, MAF, MAP, the Upstream O2 sensor, removed the CAT, replaced the standard Air filter with a K&N drop in filter(the air box was also gutted similar to in a video that I will put a link to if you want to know what I did, this was done to try to mimic a cold air intake a little more without spending the money), and lastly the intake manifold gaskets was replaced. Everything was done in around this order as well. The sensors was mostly replaced as a precaution(except for the O2 sensor), they was working fine as far as i could tell, but with the new sensors being between $5-$30, i was like, probably better to replace them now rather then getting to a point when I need them but dont have them. Since I noticed the car was running rich, I assumed it was likely the MAF, so I replaced the MAF with the original one i had, with little change, the LTFT's was looking a little better, within +/- 5.
The car has no codes shown, I disabled 2 sets of codes, mostly emission related (P0446 and P2430). The car is tuned by ZZP, and was running fine, timing seemed like it was a little too high on the later end of the RPM band (as it was picking up some knock that the stock tune wasn't, so I lowered it back to stock in some areas). My current tune sits somewhere in between stock and what ZZP has. I had changed the MAF back to stock a while back before the problem occurred again, at which point I changed it back to what ZZP had, and it seemed to somewhat fix it, but now is back to where it was before. ZZP disabled the secondary air injection system diag, I disabled the other. I already narrowed the problem down to one part, but don't want to drop the fuel tank to replace the part in question(the charcoal canister), atleast not until i need to do the fuel pump.
Below I will attach 3 files, Nov 11, shows the car running rich when at part throttle, Nov 13 shows it running closer to what it normally would, then Nov 15, showing its running rich again. For Nov 13 and 15, I went and added any and all available readings for diagnostic purposes, to see if there is something that is not reading properly. If anyone sees anything off with a possible solution, please let me know.
Also, here is the link for that video that i was mentioning, I did nearly the exact same thing, just didn't drill the hole in the side for where it can get the air flow from the fender(atleast not yet, got other problems to solve first).
https://www.youtube.com/watch?v=xFBUfYctbj8
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Originally Posted by 5FDP
