Bad IAC Valve

I am having issues with my truck idling. I will start at about 2000 rpms on warm up, and then drop to about 1500-1750 when warm enough to drive around. When I come to a stop, the rmps kinda jump or bounce around a bit as well. I have read topics about this being a iac value issue. So I took apart the entire throttle body cleaned everything, including the iac, replaced it, and now after about a month its doing it again. Should I go ahead and just order a new IAC or could it be something else?

Thanks, Dan

 

try cleaning the MAF sensor before the IAC...

as for the idle, 1500 is a bit too high for warmed up...

a lot of first gens are idling at about 600 to 800 warmed up...

 

There's a lot of chatter about that says cleaning an IAC valve will actually damage it. But if it's bad anyways there's not much to lose.

mikesDC has a good plan, try cleaning the MAF before you suspect the IAC. A little seafoam through the brake booster vac hose never hurt anything either.

 

Well I have had a dirty Intake sensor and it always throws a code. The only reason I don't think its that is because there are no codes...?

Dan

 

I've always heard the MAF with it's hair like heated wire element was the fragile one. IAC is generally just a plunger on a stepper motor.

Check the iac position. A IAC at near closed poistion could indicate that the computer is trying to accomidate for a vacuum leak. The IAC can mask a small vacuum leak but a larger one will show symptoms similar to what you are seeing.

You could also try holding your hand over the air box inlet (taking the vaccum leak out of the equation (Masking it better) and then make the IAC work / change positions as you adjust you hand to allow in more air. A smooth transistion / adjustment of idle shows the IAC functioning properly. A jumpy transition shows a sticking / bad IAC.

Watching the actual IAC positon on a scanner would make life easier.

 

Well I plan on trying all this once I get off work. The one thing I don't know how to do tho is check for a large or even a small vacuum line leak... Got any suggestions?

 

I prefer going around the top of teh engine with a 3-4' long piece of 3/8" ID hose. Place one end up to my ear and the other along the area i want to check. You can use it like a stethascope to listen to / diagnose all kind of engine noises. You can pull a vacuum line off for a test listen / this can help you find where the leak is ~ if their is one.

Others will spray liquid of some nature on the sealing surfaces / suspected leak areas. Some like to use flamabel liquid as teh engien will idle up with the extra fuel & air. Others prefer non flamabel as the engine will then idle down with less air.

For a vacuum leak big enough to hold the IAC to it's limit it should be fairly easy to find. Might also check the EGR I'm not sure what method Toyota uses for their EGR signal / check. But a gummed up EGR hung open would create an internal leak that would be difficult to find.

 

Anyone thinking a Throttle Positioning Sensor would cause problems like this?

 

Also where is the EGR valve located, ive never been able to find it