Intake Flapper (ACIS?) Grenaded Engine? 4.0 Tacoma
Sharing so others don’t make my mistake. 4.0 Tacoma 150k miles. Problem started as random cylinder misfire with cylinder 6 worse than the others. Pulled over and swapped coils 6 & 4 (first mistake). No affect.
Towed it home, then cleaned MAF (2nd mistake). Started > Engine knock that was not present before.
Borescope cylinder 6, found bolt smashed into head.
Borescope intake runners after removing, found ACIS rod snapped along threaded hole. Suspect bolt in cylinder belongs here instead of cylinder.
This probably could have been avoided if I knew about the ACIS and checked it first. Apparently this has been discussed ad nauseam on the 3rd gen 3.5, but I haven’t heard much on the 4.0 so figured I’d share my experience.
Oh and for those that don’t know, the ECU controls this flap to tune how the air flows at different RPMs to improve low end torque, and high end power.