takearushfan - 2006 FWD Base mystery engine surge multiple mechanics are stumped on

[takearushfan]

Hi all. I'm not quite sure what to do because the guys I'm used to seeing are stumped and suggested I get a full diagnosis from a different shop, which I did and he's stumped too, after 6 hours of checking everything under the sun. I'm getting an engine surge on acceleration. I can't even think of how to list all the official part replacements I've tried because I won't remember them all if I tried. I'm up to far more in replacements and diagnostics than the value of the car but I'm determined to solve this. The latest I've been told is perhaps the timing chain being a bit loose might be the issue but wouldn't the engine still surge when the MAF sensor isn't being used? I drove it around a bit without using the sensor and just using the default computer method and no surge at all. Besides, at just 87k miles my other mechanic is skeptical that the timing chain even has an issue at all. I'm not even sure what other info to provide because anything someone suggests I've probably tried but I'm posting in hopes that someone suggests something we haven't looked into. Thanks for your help. MAF sensor replaced with official Denso, up/downstream sensors replaced with recommended Denso. All live scans show nothing abnormal, smoke test found nothing (even double checking intake manifold), throttle body cleaned, power steering replaced, engine mounts secure, fuel pressure and pump fine and so much more I can't even remember, I just can't figure this out, TPS replaced, the surge is the same regardless of temperature and fuel level, same on turns as straight, lasts for about three seconds before leveling out. I just don't know what to try anymore

[Jbenrod]

If it's an engine mis-fire it should be setting a code, but no codes are being set - correct? Have the shops confirmed it's not a transmission flare or issue?

[takearushfan]

If it's an engine mis-fire it should be setting a code, but no codes are being set - correct? Have the shops confirmed it's not a transmission flare or issue?

Well, the latest thing is that yesterday, for the first time since this all started, my check engine came back on with the info shown in the attached screenshot. The initial repair was for P0171 so this latest code is a bit different. This happened after taking a 40 minute drive, the longest since this started. Only one shop did a full diagnosis and he didn't find anything with the transmission. What's interesting is the surge stops when the MAF sensor isn't being used and yesterday when the check engine came on it says one or more o2 sensors might be faulty, yet the o2 sensors and MAF were all replaced with new Densos to try to fix this issue. Can it be something as simple as the connection being perhaps lose, corroded or such? Oh and as of the latest check engine it's not surging anymore or at least if it is it's not as much for me to notice.