florider

hello all, this will be my second post, but seeing as how i posted the first one in the wrong place, this is my first post. thanks in advance for any advice, it will be greatly appreciated. my vehicle is a 99 4runner 2wd auto, 3.4 v6, 95,000 miles stone stock. the symptoms are on start up, it somtimes runs really rough right before dying immediatly. what i have been doing latley is on start up during cranking, which lasts about 1-2 seconds ill blip gas pedal just before it fires. this seems to cure the problem most the time, but not always. it does this on cold, warm, or hot starts. also, when i was driving quickly on the street, braked fairly hard for a corner, started to turn and realized it had stalled. to restart, i put in neutral and started while still moving, but it continued stalling. when it started to run proper the next corner i braked hard i for, it stalled again.i can keep it running by pushing the gas a little or bliping the throttle, but who needs that grief. when it starts and runs crappy, i can give a couple of big blips to 3-4k rpm's real quick, and this somtimes works, and somtimes not. usually it will cure itself pretty quickly so i can deal with this on occasion, but when it does this to someone else( my girlfriend )she doesnt know what to do and starts to get panicky, and nobody needs that greif. when it starts and runs good it runs perfectly, and when its bad, stumbles and dies immeadiatly and there is no in between. i have plenty of tools, am machanically inclined, can test things, answer questions you might have to help me diagnose this problem, can barley use a multi-meter but can figure it out with a little help. if you made it this far, thanks for reading. f L O

BigBallsMcFalls

99% likely it is a dirty MAF. clean it. prob be gone.

97ltd4x4

Also clean your AIC valve...located in throttle body.

TheDurk

And the throttle body in general. No CEL ?

florider

no check engine light, cleaned mass air flow about a year ago with m a f cleaner. what is an a i c valve. ill clean the maf again just to be sure its good to go. this problem cropped up about two or three months ago. ill also clean the aic valve cause it cant hurt nothin. im sure i will feel really silly when someone tells me what aic stands for, but cant come up with it off the top of my head. thanks for any and all advice, it is greatly appreciated. i will certianly post everything i try and what worked. thanks again
f L O

97ltd4x4

This is a very common problem,So I am going to do an explanation,long,but bear w/me


The IAC valve,stands for.Idle Air control valve.....
Located on the underside of the throttle body.It has 2 small coolant lines,1 large vacuum line and a wiring connector attached to it....

What it does is basically cause a controlled vacuum leak to allow the engine to idle at closed-almost closed throttle position....The coolant the runs through it keeps the throttle plate from icing up(don't worry about this)

When the trottle valve is closed(foot off the gas)...Air that keeps engine idling(running) is metered by this valve,IAC.

The computer sees the throttle position,main input(open-closed-somewhere inbetween) the engine RPM,and the Air flow data and then it desides if and how much to open this valve.

When computer wants this valve to open it controls the IAC valve solinoid,stepper motor...IE when you start engine,foot not on gas...Comming to a stop..foot off of gas...this is when it opens the valve.

When the valve opens.It allows a passage to open(vacuum) the intake port is a hole in the throttle body,just before the butterfly...the exiting port is a large hose that comes from this valve to the intake manifold(3/8" ish hose that loops by the TPS sensor.

What happens to this valve over time is that it gets gummed up,just like the throttle body butterfly valve(this is caused by the evap system dumping raw fuel into throttle body to be reburned by engine)

Ok,well,this is fine and dandy...How to fix.You have two options:

option one:
First is to remove the intake boot from MAF to throttle body,look inside the throttle body,you will see a hole on the bottom,just before the butterfly valve.You need to spray this out with carb/throttle body cleaner aerosol can w/straw...couple of seconds is fine..wait a miniute and do again..do the same to the lager vacuum hose running from the IAC to the engine manifold(will attach to metal pipe)..spray towards the IAC valve through this hose.

I would also clean the butterfly valve of the throttle body while you are in there,its probably gunked up as well.

Option two: (do a search,there is a write up on here)
get an IAC valve gasket(o-ring) from dealer.

remove throttle body(remove 2 small coolant lines,Vacuum line,electrical connector)...On bench remove phillips screws that attach IAC to throttle body(keep good pressure on screws,they like to cam out),remove o-ring,clean IAC valve,especially where it slides(can move valve w/small screwdriver,its spring loaded)...clean it out good w/ small wire brushes/q-tips,again w/ carb/throttle body cleaner...assemble w/ new o-ring,install throttle body back on vehical,ect......note:the throttle body gasket does not need to be replaced since its steel...also great time to clean butterfly valve on the bench.


Now,I have never seen it,but I guess anything is possible,that the IAC valve will go electrically open and not work at all..(99% of time it sticks because the IAC motor is not powerfull)

Hope that helps

florider

thanks for that 97ltd, that was nice and technical. sweeet. this weekend i will do all this cleaning. think ill go with new o-ring and take it apart, seems like a little more thorough. this way i can eliminate the iac valve as the issue if it continues. does "cam out" mean they strip pretty easily, so push down hard and use a proper fitting screwdriver. if so got it, if not please explain. you sound like you know your stuff. are you a real life toyota tech, or just someone who knows there stuff. thanks again, by the way, i had no idea what an iac valve was, or what it did. very cool.
f L O

97ltd4x4

Yes,by cam out I am talking about the screw heads stripping,so be carefull.

For the reccord,I WAS a toyota/Lexus tech,from 94-2003,Obtained Toyota master tech status in 1999,Lexus master tech obtained in 2002...I quit wrenching in mid 2003 to persue career change.

So,I am a bit rusty,and the newer stuff has become more complicated electrical wise,but the basics are still the same.

florider

getting advice from a tech, thats a really nice feeling. ill clean this weekend, but who the heck knows when it will happen again. last time was about a week or so ago. intermittent problems rock. so, the 5vz-fe, is it a good or great engine? does it compare to the 22re as far as its reliability? i also have a 1992 truck totally basic 2wd 5speed 22re. when i step on the brakes, the idle seems to bump up, then drop, then bump, and so on on about a two to three second cycle. any ideas. im just trying to help you knock some of that rust off man, plus my toys are sufferin a little, and i would like them in tip top shape. oh yeah, my '92 is just barely broke in at 105,000 or so. i think i need to do timing chain soon, shoot i need to do timing chain on my 4runner also at about 97,000. is that right? oh well, gotta do whats i gotta do. let ya know what happens, if anything. thanks again.
f L O

Roadtripr

I seem to running into this problem a bit too now. Twice in the last two weeks if have stalled when slowing down to stop. Pain in the neck as you loose power steering etc. I need to turn it all the way off and the give it throttle when I try starting it again. Hopefully a cleaning will solve it. Thanks for the detailed directions

BajaRunner

Here's a good pictorial on cleaning the IAC.

I've done this 2 times now, and I can feel an IMMEDIATE difference. Once you fire up the truck, its like butter.

Roadtripr

where is the pictorial? (I was actually going to ask for a few images)
This link shows a little of it but still leaves me with a few Q's
https://www.yotatech.com/forums/f123...ac-pics-92286/

Also, should the line that feeds back to the air intake be moist? If feeds back in a bit upstream of the throttle body after the intake silencer.

florider

ok all, did the cleaning, and she is idling smooth as silk. i didnt even notice it wasn't before, but it does idle much nicer now. i cleaned the iac valve and the maf. when i was taking the iac off, i unplugged the middle injector on passenger side. upon reassemly, i forgot to plug back in and tried to start maybe ten times or so. finally figured out injector was unplugged, pluged it in and it started right up. then i noticed the check engine light was on. ran it around block, it runs perfect, but light still on. will it shut itself off in a matter of time or miles. oh yeah, the problem happened two night ago again just at start-up. i really hope and believe that the cleaning of the iac valve will solve my issue. thanks again everyone especially 97ltd for the schooling on this subject, that was very nice. i will post again if i have any more problems with this.

florider

oh yeah the iac valve was very dirty and gummy with thick carbony crap. maf wasnt to bad,but i cleaned that about a year ago.

AP4CHE

pull the ecu fuse for 10 seconds then start it up, check engine light wont be on and shouldn't come back on if the problems gone, if it does scan it

florider

thanks ap4che, but i got in this morning for some coffee and donuts, and no check engine light. sweeet. i also tried to replicate the problem i was having before and am not able to. think my problem is all better. il repost if it comes up again. thanks for everything everyone. f L O

Roadtripr

Just did the easy version of this cleaning described by 97ltd4x4
TB did look pretty dirty so I cleaned that up. I only sprayed some cleaner in the hole leading to the IAC as I ran out of time (didn't take the vacuum line off and spray there). Man my idle was 2000 rpm for a bit. Went for a small trip and it started to settle back to 700 rpm (normal for me).

Did also give the MAF a cleaning while I was in there (I couldn't remove the sensor and ended up going at it via the intake instead).

Update: I have not had the engine stall since doing this

mjwalfredo

97ltd4x4, that was a great explanation. Does anyone know exactly what the function of the Air Assist vacuum hose is? Where does the other end of this hose hook up to? It looks to me like it has something to do with fuel delivery. The main reason I want to know more is because the FSM says that if you block this hose, then the engine should idle at ~500 rpm and my truck seems to always idle there when it's warm and in gear.

I've doing a super clean of my IAC right now and then will be testing the resistance later today. This Air Assist thing is the only part that is still a mystery to me.

P.S. I am throwing away my analog multimeter because it's a POS and doesn't tell me anything....

97ltd4x4

This is a nice description from a prado(4runner's name outside the US) site:

Air-assisted Injection

Prado's air-assisted fuel injection system improves fuel economy, reduces
emissions and better stabilises idling speed. It improves fuel atomisation
by combining an air stream with the fuel at the bi-directional injector
tip. The air-assisted fuel injection system consists of an air bypass pipe
|from the main idle speed control valve (ISCV) to the main injector
nozzles.

The 5VZ-FE engine's electronic control unit controls the air-assist
system, using information from a pressure sensor in the intake manifold.
The air-assisted injection system provides finer fuel misting. It also
allows for fine-tuning of the intake manifold air volume when there is a
large negative pressure in the manifold - such as when the engine is on
over-run.

mjwalfredo

Do you think it could help / would hurt the EFI system if I pulled this vacuum hose from the IAC end and poured a little bit of sea foam into it, plugged it back in to let the seafoam work into the system a little bit and then turn off the motor to let it soak in a bit?

Talk about a runon sentence Oh, and if you are not a believer in seafoam, I still wouldn't mind trying as long as you don't think it will hurt anything. I already have a can sitting out in the shed.