96 Toyota T100 stumble rough acceleration

Been lurking for a while, but I'm out of ideas on this one. Truck is a 2.7L 4-cylinder with just over 200,000 miles.

This little adventure started out as stalling on deceleration, which I believe was a rusted hard line out of the fuel tank sender and/or a weak fuel pump. I dropped the tank and replaced both. In doing that, I broke the flare end off the hard line to the engine bay, so I bypassed that with a rubber fuel hose. While I was at it, I also replaced the fuel filter and pressure regulator.

That solved the deceleration issue, but now it stumbles and runs badly up to 2000 rpm or so, then it smooths out and accelerates fine beyond that. It did have a high idle for a while, but that eventually settled down and the engine idles pretty well now. It doesn't set any error codes. I set up data logging on the Torque app, and made a graph, but I don't know what I should be looking for on it.

Graph 1 is startup and idle.



Graph 2 is pulling out of the driveway, then accelerating in 1st, 2nd, and 3rd gear, then slowing for a turn around frame 1850, then acceleration in 2nd, 3rd, and 4th. Frames 2200 through 2500 are steady speed (rough running the entire time), then slowing for a stop.



Graph 3 is accelerating from a stop in 1st, 2nd 3rd, and 4th gear, steady speed (rough running) for frames 2920 through 3190, then off-throttle coasting, followed by steady acceleration in 4th to frame 3650, then coasting neutral and back into the driveway.

Well, after a LOT of grumbling and blind alleys, I believe the replacement igniter module was no good. I put the original one back in, and the "runs like garbage at 2,000 rpm" issue seems to be gone. Lesson of the day: for Toyotas, just take the time and effort to get the Denso parts.