I've been messing with this idle issue for months now. Basically short story is sometimes it idles great, sometimes it barely stays alive and idles awful.

-i have tested TPS and swapped the first TB TPS with the second one and they both work and measure degrees fine according to my Toyofan diagnostics tool.
-I have tested for vacuum leaks and eliminated a lot of vacuum lines anyways because EGR delete and power steering vacuum lines and so on. only vacuum lines left are brand new going to brake booster, PCV, FPRs, and charcoal canister (whatever the thing on the passenger corner is
-Alternator is a brand new Denso, charges perfectly
-ECU is rebuilt
-Entire ignition system is brand new (besides igniters on the fender, but they're tested working)
-Fuel pump ECU bypassed
-IACV is spotless, i took it completely apart and cleaned it (unplugging it changes nothing though, could it be bad, which pins do i use to test it for motor operation)

other than idle the car drives great, tons of power, no hesitation, no misfire, absolutely perfect, just the idle is weird sometimes and it seems to be completely random.

only code the car has is 13 which i've tested both cam sensors to be in spec and i've replaced the wiring on both cam sensors because they were chewed up, so maybe the timing has skipped a tooth but at this point idc cz the car runs great.
if anyone has the silver bullet for this i'd really appreciate it because i'm completely out of ideas at this point.

 

I was dealing with the same problem turned out my plugs for my maf and tps where not getting signal through them and needed replaced

 

i don't think that's my problem because when i unplug either, the car either completely stalls or starts doing even weirder stuff like RPMs going up and down all over the place.

 

tried starting the car yesterday and it wouldn't stay idling at all without gas, almost like the IACV is completley closed and no air getting to the engine at all. i'm gonna try to open the IACV manually and just leave it unplugged and see what happens. maybe even actuate it manually with the pins. i honestly think at this point that the IACV is the only issue because besides cold start idles the car runs fine.

 

This is a shot in the dark but it may help. My 95 SC300 developed a battery draw that would kill the battery in a week or so if I didn't drive the car. When I jumped it it would sputter and cough and just run horribly until I got the battery fully charged and then it was fine. After a ton of searching I found out I had a corroded body ground. I want to say it's on the passenger side up by the radiator support or the front side of the wheel well hump. After I cleaned it up my issues went away.

 

yea i wish it was that easy lol. my battery is relocated to the trunk, fully charged and all grounds inside the engine bay replaced with 0 awg wire. thanks for your input though man.

 

Sounds like IACV to me. I would look for a used one to throw on and see if that changes the behavior. If you can get the connector along with it, that may be worth having in case yours is bad. Those connectors seem very prone to cracking, and gravity isn't their friend when it comes to staying in place.

 

yea it's definitely the IACV, after a few starts and stalls the car will start to idle perfectly, so once i got the idle to like 700 i disconnected the IACV so it just stays in that spot and never changes and it's fine now. yea it will take longer to warm up on cold starts but that's a downside i'm willing to live with especially since it's only a drift car. i adjusted the TPS a little more too and the stuttering and misfires has stopped too, so it's all perfect now basically.

 

I'd rather just address the problem head-on for $25, but to each their own...

 

if i can find an IACV for that cheap then i will.

 

there's a youtube video on how to rebuild the IACV, very helpful

 

i guess i can try that, i have plenty of bearings laying around already, it wouldn't hurt to try.

 

same guy, more useful videos. TPS setting is about 2/3 of the way through this video


and a quick in car check on this video