Reckless

iTrader: (9)

Car aws idling around 1100 in park, even with 600 rpm set for desired idle in LS1 edit. I pulled the intake yesterday to ensure there were no vacuum leaks. I cleaned up everything and resealed everything. There are no vacuum leaks.

IAC counts were around 75, so I started drilling. Drilled and drove around for a while. IAC counts came down, but the darn idle kept going up!

Here's the problem:

The more I drill, the lower the IAC counts get, but the idle keeps rising due to the extra air coming in through the hole!

Is there some other way to control the idle that I am totally in the dark about? <img border="0" title="" alt="[Sad]" src="gr_sad.gif" />

ChrisB

IAC counts are a measure of how much air the computer is "bypassing" (coming into the motor regardless of butterfly position) - the higher the number the more air is coming in.

Now it takes a certain amount of air to maintain an idle with a given displacement and rpm. When you drill the hole in the tb blade larger you are offsetting the air that is coming in, so the computer doesn't need to "bypass" as much are through the iac, so the iac counts lower. This is normal.

Now if your desired idle is set lower than your actual rpm, and the IAC is staying at 75 (it's range is 0-160) something is wrong - it should close itself until your idle drops - and if your hole is too big or your butterfly blade is stuck open and preventing you from going lower it should rail itself at 0.

My first guess is that you might have a faulty temp gauge - this will keep you in a cell in the desired idle table that will keep the idle at 1100.

In autotap "desired idle rpm" is a value you can log I believe. Log it and verify your desired idle isn't set to 1100. Also log your rpm to verify your tach, etc. isn't off.

If your desired idle rpm is lower, your IAC isn't railed against 0, but your idle is still staying high then I would try and borrow someone else's TB/IAC assembly.

Chris

Reckless

iTrader: (9)

Thanks Chris....I was starting to think the IAC sensor is fouled myself. The blde isn't hanging open though. The TB id from a truck, and I can't remember if I changed the IAC from my old TB onto the new one. Wonder if they differ?

I will log the desired idle and engine speed.

Which temp gauge are you referring to? I'm pretty sure the temp from the head is fine. I've been watching that.

Todd

Pro Stock John

iTrader: (34)

What is your TPS in drive? Mine is too high, I need to close the blade, I have it cracked a bit.

Also a vacuum leak will cause it to idle around 1100 I have done that (two years ago a pcv hose was cracked).

Reckless

iTrader: (9)

OK guys....I just logged about 10 seconds at idle. Everything is fine it seems. It isn't a vacuum line. I went to each one and clipped the line with pliers to confirm.

As I mentioned above, even when I drill out the TB blade, the IAC counts barely fall and the idle just gets higher. That leads me to believe Chris was correct. Something wrong with the IAC motor. It isn't adjusting properly.

Fortunately, I have an extra TB blade laying around. Last night, I had the hole drilled to 1/4" and the car was idling at 1500 with IAC counts of about 65. While the IAC counts were about 12 lower than now, the holw was considerable larger than the blade I have in now.

Here is what the ATAP looked like:

Timing >>> 29.5 to 30 degrees
RPM >>>>>> Approximately 1050
Temp(°F) > steady 187F
TPS >>>>>> steady 3.1%
MAF Rate > 1.53 to 1.55
IAC >>>>>> steady 77

I suspect the IAC motor. I can swap my TB with another guy this evening to compare.

Todd

Nick's WS6

There are 2 values you can look at in Autotap called "Desired IAC" and "Desired RPM". Check thoes two against what is being reported in real time.

Reckless

iTrader: (9)

Desired RPM was what I programmed - 600rpm.

I don't think my IAC plunger is bad. I swapped IAC's with a friend last night and there was no change in idle.

Guess I will just set everything up for a 900-1000 idle and live with it <img border="0" title="" alt="[Sad]" src="gr_sad.gif" />

Todd

jimmyblue

iTrader: (11)

If your IAC drops when you drill then that
indicates it's still closed loop, because
it's correcting for the increased air.
Something else is commanding a high idle
setpoint. A vacuum leak is the same effect
as the drilling. There has to be some other
input that's keeping you off the hot idle
value, seems like.

wrencher

iTrader: (2)

Are you sure you don't have a vacuum leak? Use this method to help you find vac. leaks, regular propane cylinder, with torch take tip off and put a vacuum hose over the end (2 foot will work) turn propane on and sweep over potental areas for leaks. Usually when you hit a vac. leak (on a f. i. engine) it will idle down a little rough but definetly noticable. This is the easest way to find elusive vacuum leaks. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />