i heard about a test u can do to check if the IAC is messes up. my car idle surger from 1000-1500, what are the tests, i heard of one where u plug a hole in the TB and if the car doesnt stall then u have a vacuum leak, but what if the cars stalls, or worse the car dies. what does that mean.
the reason i ask is because when i plugged it the car died.

 

up

 

One test is to just unplug the IAC while the car is running and warmed up and if that does nothing, your IAC is messed up, if it changes your idle, its fine.

 

i have heard many diferent versions of that test, i heard that if the idle drops then it messed up

 

Your car is suppose to be able to idle on its own withOUT the IACV. It is referred to as the "base idle" and is usually 500-550rpms. The IACV can only add air and so when its plugged in, it will raise the idle to about 750rpms, referred to as the "curb idle" speed.

So when your car is fully warmed up, and you've got the surging going on, unplug the IACV....the idle should drop to 500rpm and become stable.

 

right but when i reset the ecu and plug it back in it stull surges

 

You've got a vacuum leak somewhere.

So, what happens when the engine is surging and you disconnect the IACV? Does the idle drop and become stable? If yes, then your IACV is not at fault.

The ECU has a fuel cut on decel strategy to save gas. Basically, when the TPS shows the throttle closed and engine rpm above ~1100rpm, the ECU cuts the injectors off. When you have a vacuum leak, it will allow the engine to rev above 1100rpm which in turn will activate the fuel cut strategy. So the fuel injectors get cut off, engine rpm falls below 1100rpm, fuel injectors back on again, engine rpm goes above 1100rpm....wash, rinse, repeat.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by EE_Chris &raquo;</TD></TR><TR><TD CLASS="quote">Your car is suppose to be able to idle on its own withOUT the IACV. It is referred to as the "base idle" and is usually 500-550rpms. The IACV can only add air and so when its plugged in, it will raise the idle to about 750rpms, referred to as the "curb idle" speed.

So when your car is fully warmed up, and you've got the surging going on, unplug the IACV....the idle should drop to 500rpm and become stable.</TD></TR></TABLE>

Now what if it drops, but not to 500 rpms? Then you have a vaccum leak? The IACV is bad? If you plug the IACV back in while the car is running, it's going to stay at that idle until you restart your car...i tripped an ecu code and the car idled at 2000 rpms since it surged from 1200k to 2200k wtf?!

 

what about the TB hole test???
and where can i check for the leak??

 

If it drops and becomes stable, but does not drop low enough (500rpms), then yes, you could still have a vacuum leak. However, it could also be something simple, like the idle air bypass screw or throttle blade stop screw was tampered with which has already raised the base idle speed.

So, assuming the throttle stop screw wasn't touched, and your TPS output is ~.45v @ idle, then use the idle air bypass screw to lower the idle some.

The IACV has a window of base idle speed with which to work on....so it can't be set too high.

And just to note, when I say 'vacuum leak'....the idle air bypass screw creates a leak of a sort. So don't limit thinking to torn gaskets and the like. Stepping on the throttle creates a really big vacuum leak as well.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by S.Convoy &raquo;</TD></TR><TR><TD CLASS="quote">what about the TB hole test???
and where can i check for the leak??</TD></TR></TABLE>

What throttle body are you using anyway?

 

This throttle stop screw you're talking about, could this be effected if i messed around with my throttle cable? If so, i think it's the stop screw then that's causing all of this. Is there a way to redo what i did wrong?

Also, i'm checking the FIV for leaks since i heard these go bad after awhile.

 

Your throttle cable attaches to the throttle rotor. This rotor has a screw which will hold it open slightly. If your throttle cable was too tight, this screw would have no impact, as now the rotor isn't even tounching it. The throttle rotor is attached to the same shaft that the TPS is on...so any movement here will result in a shift of the TPS output voltage.

And yes, FITV's do get 'lazy' in their operation.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by EE_Chris &raquo;</TD></TR><TR><TD CLASS="quote">If it drops and becomes stable, but does not drop low enough (500rpms), then yes, you could still have a vacuum leak. However, it could also be something simple, like the idle air bypass screw or throttle blade stop screw was tampered with which has already raised the base idle speed.

So, assuming the throttle stop screw wasn't touched, and your TPS output is ~.45v @ idle, then use the idle air bypass screw to lower the idle some.

The IACV has a window of base idle speed with which to work on....so it can't be set too high.

And just to note, when I say 'vacuum leak'....the idle air bypass screw creates a leak of a sort. So don't limit thinking to torn gaskets and the like. Stepping on the throttle creates a really big vacuum leak as well.</TD></TR></TABLE>

I know this is an old thread, but it's the only one I found very relevant.

I installed a NEW TPS, and for the throttle closed output to be ~.45v, I had to slightly adjust the throttle screw.

So now the TPS is ~.45v/4.5v, but it's searching for an idle and it's throwing the IACV code. I unplugged the sensor with the engine running and the idle dropped to about 500 rpm and leveled out. With the sensor plugged back in it surges from 1000-1500 rpm.

The IACV came from a running, No CEL throwing code, so I don't see how it could be bad.

I can't find any vacuum leaks in any hoses, but I'm not really sure about a good method to find them.

 

ok so ingot a 94 civic ex fully built motor and turbo .i replaced the iacv and start the car it still reving to 1400 and when i unplug it and plug it back in it idles smooth and then the second I press the throttle and let it go back down it will start reving at 1400 again? Wtf I'm stumped.also checked for vacuum leaks and found some and fixed .

 

16 year old thread. Please start a thread with all your car information and issue, and if you desire, reference this thread instead of necro hijacking this thread,.