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