Hello,

This past year I "finished" my 1UZ swap (1994 LS400) into a 2nd gen (1995) 4Runner (4x4, R150F). I put "finished" in quotes because while the engine is in the truck and the truck does run (and even drive), I've been battling a poor idle situation for 6+ months. Revs up and drives just fine, but as soon as I'm back down at idle, it barely stays alive and eventually just dies. Makes no difference if I let the engine run for 5 minutes to warm up/get to operating temperature. I'm not a believer in the "parts cannon" approach, so I've been methodically eliminating variables, but I've run out of ideas.

Here is a recap:

First thing I did was check error codes. Got 71 and 31. 71 is EGR malfunction, which makes sense as I deleted EGR. 31 is "MAF", likely unmetered air.

With a code 31, most likely culprit is vacuum leaks. I tested for leaks using a smoke machine. The smoke test did in fact reveal several serious leaks due to old rotting vacuum and PCV lines. As I replaced lines, I ran the smoke machine multiple times until absolutely zero smoke came from anywhere. Vacuum leak sorted.

Problem didn't go away. Still poor idle, wants to die unless I give it throttle. So, I tested the resistances at my TPS, ECTS, and MAF according to the factory service manual. All resistances, voltages, grounds, etc are within spec. Based on that, I didn't see the need to replace them "just because." Tested for wire continuity between these sensors and their respective pins on the ECM. Normally if a wire was broken somewhere you would get a CEL for the affected sensor, and I wasn't getting any other codes, but I still tested just in case. No surprises there, continuity all the way through.

Next, I investigated my IACV. I confirmed that the resistances were good, but it seemed the bearings inside were gunked up enough that the plunger wasn't engaging. So, I purchased a rebuilt OEM IACV. Tested by applying voltage, and the plunger moves. Installed that new IACV. Problem is still there.

Next, I did a review of all of my grounds. Checked every single ground according to the EWD, all are tight but I re-cleaned them for good measure. Used a multimeter on every single one, no issues. No change in idle.

Then, I re-visited my swap wiring. After reviewing the EWD and re-reading through various forum threads, I realized I made a mistake in my swap wiring. I was using ignition power to open my EFI main relay instead of the MREL pin on the ECU. This is important because the MREL pin continues to send voltage even after the key is off, which is necessary for various engine sensors to reset/recalibrate etc. So, I corrected my wiring, tested voltages and...same problem. Poor idle.

That brings us to the present. Really sucks that it's just sitting here and I can't enjoy it, especially when it's so close to being done. Any ideas from other guys who have successfully completed this swap would be appreciated. Attached is my wiring diagram for reference.
Thanks