Hey guys, having kind of a unique issue and thought I'd try here to see if anyone else has had a similar one. I have a 2011 LE. 120,000 miles, bone stock aside from a 2" lift and some wheels/tires. I've owned this truck for about 8 months now, and have never had an issue. Recently, I was pulling into the local pew-pew range, which has a steep decline leaving the highway into the parking lot. Another car was coming out, so I stopped and pulled to the side so he could pass. Once back on level ground, I noticed an odd stumble/hesitation. On the way home, it turned into a full blown misfire, and got a CEL with multiple misfire codes. I checked all the plugs and coils, which seemed to be fine, but I replaced them anyways (Denso coils and plugs) as at this mileage they were unknown age.

Fast forward a few days, and I pulled off the side of the road for an ambulance. Was off camber for a few seconds, but when I pulled back on the road, another stumble and hesitation. Filled with fuel later that day, and didn't have another issue for about a week. Leaving another store up a somewhat steep incline, it stumbles and hesitates again. The stumbles and hesitations only show up when the tank is under about 5/8 full. I put a clear piece of hose on the hard fuel line in the engine bay, and when running just the fuel pump off 12V it looks good until pumping the fuel down a bit. As the tank gets lower, I see more air bubbles in the fuel line coming from the pump.

My question is, has anyone seen this kind of issue before? I searched and found nothing on all of Google describing a similar problem aside from a single thread on a Tacoma site describing air bubbles in the fuel line. It almost has to be something in the pump/suction assembly, so I've ordered a new Toyota unit. I'll update more once I get the part replaced, but figured I would check and see if anyone else has seen this happen before. I did pull the tank already, and pulled out the pump. I ran the pump out of the tank in a bucket of gas, and saw no leaks in the lines. Obviously I can not replicate the conditions in the tank exactly, but my only theory is that when the tank level drops low enough, either the "fuel bowl" that the pump sits in goes partially dry or a very small hole in one of the hoses causes a venturi and sucks air in (this makes no sense to me, as a pressurized line should leak outward not suck air in but it is possible). The fuel return line dumps into the bowl, so not sure how it would go dry. Maybe the return has a hole and brings air to the bowl, then gets sucked up in the pump? Idk guys, I'm open to any theory y'all can muster.