1st Gen Taco Troubleshoot

I have an 04 Tacoma, 2wd 2.4l 2rz-fe that I just recently did a head job on and am having some issues with idle now that the motor is back together. Overall the rebuild went fine and on the first turnover of the engine everything fired up and was looking good but I realized it was idling at a high rpm (doesn't have a tach so guessing around 1700 rpm). Found what I thought was the issue, the cylinder 4 injector somehow lost the insulator gasket and the vacuum leak was coming from the injector port...easy fix. Slapped it all back together, fired it up and idle was back down into the normal range (750 rpm). Let the vehicle idle to get up to operating temp and wanted to monitor everything since this was my first rebuild with this vehicle and everything seemed fine, no issues. Within a couple of minutes the idle shot back up again, fml. Got out the can of ether and started checking the vacuum lines/intake/throttle body/plenum. For context, I have been doing this build on a budget and don't have time or the money to get the vacuum leak diagnosed by a shop so going old school here. So in my frustration, I pulled the car out of the garage and decided to drive it a short distance down my road to see if anything would change. Still idling above the normal range for most of the drive (1/8 mile) until I started getting crazy idle fluctuation. Shifted through gears fine, seems like the engine was operating normally outside of this issue with idle. At this point, I pulled it back into the garage and left it in neutral where the idle continued to fluctuate pretty dramatically. Shut it off, time to do research. After some time looking at this issue online, it seems like this could potentially be the IAC?? The engine rebuild took about 2 months as I am a full-time student/working etc. and so the IAC was sitting on a shelf. Took the IAC off and noticed a lot of corrosion/ build-up from the coolant and decided to do a cleaning of the valve (I know, not recommended) and put it back together. Idle fluctuation was still there. Disconnected the battery, disconnected the IAC to see if things would change, reconnected the battery, and fired her up. Idle was way back up again but without the fluctuation. So I am at the point where this would make me believe the IAC has gone bad but was also wondering if the TPS might have something to do with this? Anyone have a similar experience with this issue? While driving I didn't have any issues with throttle surge or hesitation and seems to only be an issue when the vehicle is in neutral. Any suggestions would be very helpful at this point! TIA...

 

Welcome to TW! I do not have the 2rz, but I do have the 5vz, so please excuse if I may be incorrect on my information, and maybe someone may be more help to you than me. My guess would most likely be the IAC, and you should test that with an ohm meter. I would see if you can track down a FSM for your truck, and look at the testing procedures for testing the IAC and TPS etc. In my experience the IAC is very sensitive, and even after I cleaned mine my idle was around 2000 rpm, and was only fixed by replacing it, and this was before I had an ohm meter so I wouldn't know if it showed out of spec, but it most likely would've. Just test before throwing parts at it, since it seems like you have tried to reset the ECM by disconnecting the battery. Hope this helped!