rough idle

OK, this has been posted before. There is no separate IAC on 03+ 3.4L V6. everything is one TB unit due to the motorized assist/TPS. This is why you have to buy the "entire" unit from Toyota (if you go that route).

http://www.tacomaworld.com/forum/1st-gen-tacomas/324673-3-4l-w-etcs-tb-cleaning.html

There are places on the "universal" 3.4 plenum that do not have hoses connected and look open but are just unused.

my issue still persists with sometimes low idle (I've dropped to 350 rpm a couple times) and sometimes high (1k-1200). going to try and change all the vacuum lines this spring when it gets warmer.

 

Ya!!! Thanks for the confirmation! Thats what i thought.

 

Yes, I just found some other threads asking if these 04 engines have an IAC. Is there a valve in the throttle body that can be cleaned, like by spraying cleaner into a port?

 

Btw what is etcs?

 

I'm unclear if you have an erratic idle versus a rough idle. An erratic idle would be an idle controller or possibly a vacuum leak. For a vacuum leak you can inspect your hoses or use a spray bottle of water to spray around the houses to see if the idle drops after spraying with water. The water fills in the cracks & causes the idle to drop.

If it's a rough idle, and it essentially runs fine otherwise, then it's likely a motor mount. This will exhibit as more vibration at different idle speeds. For instance things may be fine at idle in park with a slightly lower idle, versus stopped & in drive. Or stopped with the AC on.

You can generally reproduce this by staying in park & using the gas to idle to the RPM that causes the vibration. It may be fine at 650rpm, but rough at 750.

My rough idle went away after replacing my engine mounts (3rz engine though). The engine mounts had fine cracks where the rubber was bonded to the metal plates. I suppose after 15 years they were a little old.

 

Its rough at 650, not erratic or high like a vacuum leak. BUT NOT VERY BAD. Its ever so slightly rough. I mean like BARELY. I don't think its a motor mount. Just cause of how slight it is, but ive been known to be wrong..

 

Electronic Throttle Control System (the motorized assist is also the cruise motor mounted behind the TB)

didn't find one when I did my cleaning but I also did not take off the rear cover. the tubes under the TB are for the coolant so I didn't spray anything in them to prevent contamination of the rest of the system.

 

Cool, thanks a lot for clearing this up! I feel like an a$$ for not finding your thread on this..Now its time to seafoam soak the cylinders... Well actually tomorrow after i buy some oil for the change! After i do that i will report back my results...

 

From an 01 FSM but it also shows it in the 03 FSM.

 

Double check and make sure you didn't break a plug boot off on a spark plug, i made the mistake of it when i was putting mine back in after fresh plugs, and it started shaking at idle, but never threw a code like yours. Also double and triple check all vacuum lines. even the tiniest crack in a line could cause this. An easy way to see, is spray break cleaner on each one, if you see bubbling, replace that line. Clean your MAF Sensor extra precise, even the smallest particle will throw it off. Make sure your Throttle Body Gasket is good (on the intake side, the only gasket), a little bit of un-metered air will cause a hiccup in the idle, but still no code. Even a bad o2 sensor will cause a rough idle enough to kill the engine. Also make sure everything is plugged in on your transmission, and that your Trans Temp isnt too warm (usually if it is it will show you a "AT Oil Temp" light next to your Diff Lock light, and that will sometimes kill your vehicle). Look for the most minor issues first. Goodluck and keep us Posted!

 

I'm going to still say motor mount. Only because my last two experiences with slight shakes at idle were motor mount issues ('96 fzj80 & '00 Tacoma). The roughness was *only* at a certain RPM range.

My motor mounts weren't broken, they just transmitted slightly more vibration than they did when new.

Regardless, it doesn't sound too bad. You could just live with the issue & ignore it.

 

so the IAC or ISC valves are the items that are often the cause of rough idle because they control ther idle air mixtures your engine gets.

do you have anything that looks like what is shown in the pictures above?

the way it works is engine coolant runs through the tubes so it can pick up the engine temperature and based on that temperature the air valve opens or closes to adjust the extra air going passed the valve body butterfly flap at idle

 

This is an interesting thread. Dealer says 'no IAC'. Online parts houses don't agree on it. Googling. I found a comment that electronic throttle (non-cable) engines don't have an IAC.

Maybe Toyota has a different name for that part that does what IAC does for your truck. Next time you call the dealer, ask to talk to one of their mechanics, who may know more than the parts guy.

 

im pretty sure the IAC was replaced with the ISC but I cant tell you the year it happened so you have one or the other but you do have one.

 

pretty sure he mentioned it in a previous post, but that manual is an 01 so it's a little different

ISC = Idle Speed Control?

I believe they switched production early "during" the 2003 year when the last of the 4Runners were done and gone if memory serves (think a few '03 had the previous TB)

 

ISC and IAC are different names for essentially the same thing. They are not found on the OP's 3.4. He has the ETCS that does most of the "controlling", there is a throttle cable that does play a part.

The rectangular plate on the top of the t-body with 4 Phillips screws covers a chamber containing a row of holes into the t-body just before the throttle plate. This chamber has a hose leading to what Toyota calls the "air assist system". This is nothing more than a system of 6 passages that end just upstream of each injector. At idle these passages allow manifold vacuum to suck a fixed amount of air thru the passages and direct it at the injectors .
This helps to atomize and mix the injector spray at idle, while airflow in the intake is minimal. Toyota says "For better idle quality".
It's not likely but it is possible those holes (in the t-body) could be gummed up. Pull the 4 screws and take a look.

The engines with an IAC valve split the idle air into both the air assist and and a passage bypassing the throttle plate into the main intake. The ECM controlling the IAC valve determines the idle/fast idle speeds by controlling the air (under vacuum) let thru and delivering the appropriate amount of fuel.

My understanding of the coolant lines on both types of t-bodies is to prevent "icing", the same applies to the black foam cover where the PVC hose connects to the intake.

 

Nagorb: yes i looked at your pic of the manual, no there is nothing resembling the iac or icv... Sorry.

Chrish: im about to just start thinking maybe you are correct, besides ive already been living with it for a while now..

Tan4x4: when i went to the dealership yesterday to pick up the pcv grommet i asked to speak to a tech, and the parts guy, ever so politely, said they get paid to work on cars (thats for the dealership)

98tacoma929: same thing happened to me when I was removing the plug wires. The metal clip broke off and stayed on the spark plug. Happened twice. It was a bitch, but i got them off. And managed to replace everything. When i do the seafoam this weeend im gonna soak the cylinders over night too, maybe... I also intend to go get a can of carb cleaner so i can check for vacuum leaks.

Deadpool: i removed that plate you mentioned when i cleaned the tb. Come to find out there is no replacement gasket for it eithe, go figure. Needless to say as of 3000 or so miles ago it was spotless.

To everyone: thanks for all the input..

 

well that sucks lol

if it was me I would have just walked around the outside and walked into the shop area and ask someone there if they had a second to answer a question.

the parts guy was just being an ass, maybe he was a manager or something, they love to be pricks

 

Update. Seafoamed through the pcv valve. Watched an entire episode of top gear (British version) while the seafoam did its magic. Just took the truck for a spirited drive. seams to have smotthed the idle a bit. I tried to hit every red light on the way home. Got to the house and just kept the truck in drive whith foot on the brake. Its definitely smoother. not perfect but better. I have half a bottle left. Thinking of doing it again. Scratch that, just did.

 

Ok, another sitrep. Seafoam didn't smooth out my idle that much, maybe a hair, and to be clear i DID NOT soak my cylinders, only introduced the seafoam through the pcv hose. however, i was taking the advice of whoever mentioned a vacuum leak and was spraying down all the vacuum lines and such with carb cleaner, and found no leaks. Then i was fiddling around again with the pcv and this time the damn "new" O'Reillys special broke in half. piece of SH!T. Cost me a 40 minute round trip, and another 10 bucks from the dealership.
Purple pcv is oem, brown is crappy O'Reillys.



Fwiw, buy oem!