It is almost like clockwork every time. I will start it up when it is cold and after about 2 minutes it will begin to surge for about 3 minutes and then once it fully warms up it stops.

 

Installed new coolant temp sensor and it has not surged yet but it was warm when installed and it doesn't usually surge then so I will wait until it is cold and let you know how it goes.

 

Temp sensor did not fix surging issues. I broke down and brought the truck to a local guy who is very good at this type of stuff. I am sick of freezing my ass off outside working on the truck and it is driving me insane! I'll let you know what I find out.

 

Good luck to you and I'm sure you will, but please do make sure you post if you ever do figure yours out. Right now I am looking to buy another throttlebody and start from square one after checking everything installed or that I will need to install new. I too live in a freezing environment and don't have the option of wrenching on this truck without freezing my butt off which only adds to the frustation.
I will probably try pulling the rubber air duct and place a piece of tape on the 'port' for the AAV/IAC/IACV or whatever the proper name is for it. It's worth a shot since I am pretty much convinced that it isn't functioning as it should be. Right now I'll take a half-assed fixed over a truck that I can't stand driving daily

 

I will definitely keep you posted I know how frustrating this is. I have been trying to figure it out for almost three weeks to no avail and I am just sick of messing with it. I have already fixed almost every possible known cause I can think of.

1. checked nipple that goes to IAC valve...clean as a whistle
2. pulled off throttle body and IAC valve...clean as a whistle
3. took of both lines to IAC to make sure they weren't plugged...clean as a whistle
4. changed leaky radiator and flushed coolant...still surging
5. changed coolant temp sensor...still surging

The only thing I haven't changed is the IAC valve which I just don't want to spend $130 if that won't fix it. Although it was clean the wax bead inside may not be functioning properly. But they guy who works on my stuff doesn't charge diagnostic fees like we do at the shop I work at so I am letting him have it for a few days. As soon as I know what's going on I will let you know what it was and if it fixed it

 

Egr stuck open? Causing air to come in? Idle set too high..?
Exhaust leak before o2 sensor?
Bad o2 sensor?
Start pulling codes.

 

FWIW, I decided after work today that I would try exactly what another member here did by eliminating the idle air valve by placing a piece of tape over the hole. It took me less than 5 minutes start to finish, a heck of alot less time than I've had wrapped up in pulling my hair out trying to do several other things that didn't work
I simply sprayed some brake clean on a rag and wiped up the area around the 'port' to the IAC (or whatever the tech name of it is considered on Toyotas) and put 2 layers of the shiny foil tape used by heating and AC contractors. I reinstalled the boot and started the engine and (which was still at normal operating temp. from my ride home from work minutes before) noticed immediately that I had an idle WAY lower than I did before. I am going to relate this to the fact that I had the 'idle adjustment screw' (flat head screw on top/left of TB when looking at it from the radiator) screwed all the way in but this is what I had to do earlier just to get the idle at or around 1200 rpms. When I first started the motor after installing the tape it was barely wanting to idle at around 400 rpms by the dash tach (so take that for what it's worth). I then loosened the 'idle adjustment screw' until I got the idle right around 900 rpms. Took the truck for a drive and it ran perfect. It didn't hang at 3000rpms for a second before dropping to the 1500-2000rpm up down idle stunt when I pushed in the clutch like it has ever since this problem started. Also, the truck doesn't have the "clunk" feeling a second after I let of the throttle like it has done ever since I've owned it (only less than 2 months/1500 miles).

I am fairly certain that this has solved my idle issues, even if it isn't a remedy recommended by any toyota manual. My last test will be to wait for the engine to cool all the way down and try a cold start situation and see what happens. I already see that it has cured all the issues my truck had running it before at the same engine temp as it was during my test drive after installing the aluminum foil tape. I will post again here in a few hours once I am certain the engine is completely cool again (it shouldn't take long considering it is only like 15 degrees out right now).
Here is a pic of what I did:



I bought another throttlebody last night and I am waiting for it to get here, but honestly if this cures my idle issues I doubt I will go through the hassle of trying to swap out the TB right now with the weather.

 

im having idle troubles too, mines low when cold and high when hot, searching tells me its probably the IAC, but for the life of me i cant find a picture of it to know where it actually is, can someone PLEASE post a pic pointing it out for me? thank you. thread jack is now over.

 

I'm by no means even to a point where I'm comfortable owning a toyota with my lack of knowledge on them, but I do know that the IAC is at the base of the throttlebody somewhere. A coolant line goes in the front and I guess one must go back out the rear (I have a hard time seeing anything very clearly the way everything is packed in so tightly ). If you look at the pic I posted above, you can see the air hole that is covered by the shiny tape which has to lead to the IAC which has to be at the bottom of the TB.
Hope this helps, sorry I am a toyota newb.

 

I found a pic online and added a RED circle to what I would think is the 'cover' for the IAC. Also, I believe the coolant flows in the front and out the back just like I have the arrows drawn in (someone please correct me if I'm wrong). Note that the TB is actually upside down in this pic so you could imagine how packed in it is when installed and how the 'cover' would be in a position (facing the firewall) so it would be impossible to inspect with the TB installed on the motor.






UPDATE* On blocking off the IAC it does effect the starting slightly by making the motor turn over an extra turn or two before it fires. At that point the idle was pretty low at about 600 rpms but it still would idle just fine considering it is probably about 8 degrees here right now. Once the motor got to operating temp, it idled right at 900rpms like I had it set before when it was warm I actually LIKE the fact that my motor isn't idling at almost 2000 rpms when the oil is like molasses in the bottom of the oil pan. Took it for a 6 mile trip and truck ran better than ever since my ownership. The IAC is a good thing to have I'm sure when it is operating as it should be, but since mine isn't I am MUCH happier with what I have now. No more bouncing rpms from 1500 to 2000 everytime I come to a stop and that horrible "falling on it's face" clunk when I let off the throttle is completely gone.
We still have another 2 months of winter at least here, so I'm happy

 

I had the same problem on my 91. On mine, there is a ground wire that goes to the engine block on the drivers side into the wiring harness (best I can tell it goes to the ECU). Due to getting hot and cooling back down over time, that wire had become worn out (very brittle and some strands broken inside the jacket). I never would have noticed it had I not dropped a wrench and it broke, then it wouldn't even start. I replaced about a foot of that wire and BAM....no more idle surging. I would say that the wire I'm talking about is to small of guage wire. If it happens again, I will run bigger wire to werever it goes. I can post a picture of the wire if anyone would like to see what I'm talking about.

Just saying...That fixed mine.

 

well i was outside trying to figure it out and i did! i deleted a bunch of crap from the motor during the rebuild and one of the vacum lines went from below right beside the idle screw to the intake, turns out it was letting massive amounts of air into the intake that shouldnt have been there, took the line off, covered the holes with some trusty duct tape, and she runs like a charm now!

EDIT: also, think its bad that the coolant line coming out of the IAC is plugged? im about 80% sure mine is lol

 

I heard from the guy at the shop and he seems to think that my mass airflow sensor is the cause of my issues. I am not so sure I buy that but he seems to think that everything else is fine. He has never steered me wrong so I am going to find one secondhand and see if that fixes the issue. From what I have heard on here there are so many different things that cause idle surging!

 

Yeah a picture would be awesome. It is nice to see people here chiming in with actual comfirmed fixes instead of just throwing around a bunch of guesses. This seems to be helping a lot of people. If only I can get mine straightened out.

 

Thats it center of the picture. Goes from that point into wiring harness on the drivers side frame rail. When I got the truck it was under a manifold bolt.

 

How could you tell it was broken if it is covered? I know exactly what wire you're talking about too.

 

I dropped a wrench while working on something else, the wrench hit that wire and broke it off. it was that brittle!!! If yours is hooked to the manifold bolt you could try skinning a spot back a couple feet and jumpering it to another place on the engine. Might fix the prob, might not. It did on mine, thats all I'm saying.

 

All I know is that this engine has a serious f'ing problem with idle surging issues. What is more frustrating is the ridiculously large list of things that can cause it to happen. Thanks for the info it is one more thing to check and try...

 

Yea, to be such a simple motor, all the crap around them can make them complicated. Take your time, getting pissed and in a hurry will never help. That's coming from experience. I've thrown enough wrenches to supply a snap-on truck. You'll find the problem, it's probably right in front of you.

 

So I brought the truck to work today and brought it in the shop. I let it warm up and sure enough it started to surge. I put duct tape on the IAC port on the throttle body...no more surge. I had to adjust my idle up a bit to get it to run properly but it runs good now...no surge. It will run a bit rough for a second or two on initial startup but it comes right out of it and idles smoothly. I haven't taken it down the road yet but I plan on trying it to see how it goes. It is very cold here like 10 degrees right now so it will be interesting to see how it reacts to a cold start. If it runs fine I am going to find a better tape to block it off with and leave it like that. I will keep you posted.