Zee man

I have been having some IAC problems. I am on my 4th IAC motor. I can use my laptop to watch the IAC numbers, when the IAC is bad they are all over the place, from 9 to 80 instantly then back again. Sometimes it will reset and be good for a while, sometimes not. So, I replace the IAC and its ok for 3 maybe 4 days then I get a little surging at idle. Then it gets worse, It just does what it wants to when it wants to. Also when it is acting up the tach starts twitching... Yeah, I know, but I can watch the tach jump and when I see it twitch I know an "episode" is coming.

So I was thinking about it. Maybe I am coming at this from the wrong side of the problem?
What do the IAC numbers represent? The current position of the IAC motor Or the position the IAC is being ordered to be in? And what controls the IAC? It has to be reacting to something?
I feel like the answer is just out of my reach here.

Injuneer

The IAC "counts" you see on a scan are is the numbers of steps the PCM is telling the IAC stepper motor to position the pintle at. There is no feedback to the PCM regarding the actual IAC position. So it is the PCM direction only.

If the counts are jumping all over the place, its most likely in response to input to the PCM regarding coolant temp, throttle position, vehicle speed, etc. Now if the IAC is opening on its own for some reason (electrical short?) and idle RPM is going up and down, the PCM will lower and raise the counts to attempt to move the valve and correct the RPM.

But I wouldn't take what you are observing on the scanner as an indication of an IAC motor fault. If the tach starts "twitching", it's possible the high resolution pulse signal from the optical cam position sensor in the Opti is corrupt, and the tach, and the PCM's directed IAC counts are responding the the erratic RPM signal. A data log might show the erratic RPM signal.

Zee man

I am not real computer literate. I am going to have to figure out how to do that. I have several saved logs. I know I have to copy them over to paint but after that the site says I need to shorten the message.

Zee man

Zee man

this was a shorter log I did today when the new IAC started to go nutty. I hope you can use that Fred.



I think I figured it out better, hold please

Zee man

Zee man

Image - TinyPic - Free Image Hosting, Photo Sharing & Video Hosting

Injuneer

A .csv file that I could manipulate with Excel would be a lot easier to look at. Right now I'm on my phone, so there's not much I can do with the photos.

Zee man

Sorry about that Fred I dont have the foggiest idea what a csv file is, let alone how to provide it to you.

Zee man

I did notice under the target idle column it showed 1388 instead of 675 a couple of times , I thought that was odd. tps hadnt moved from 0.

This is a brand new MSD unit too. I am going to try and post a link to pic of the entire log. Its all I can do at this point, it may or may not work.
http://i58.tinypic.com/2mcc76f.jpg

97WS6SCharged

The only oddity I'm seeing is at one point the computer demands an idle of 3188 instead of the normal 675 and at the same time it looks like the car stumbles for a split second then the idles shoots up to a little over 1000 and gradually settles back to 700. What's been done to the car?

Zee man

It has headers and an ory, egr delete, tuned out, air delete, also tuned out. New plugs, wires, cap, rotor, MSD distributor. Its the new redesigned unit.and new o2s. 160 T stat, the fans have been tuned to come on earlier. new temp senders. New water pump. New lifters. New head gaskets.


That oddity, the 1388 happens again later durring this log.. I see it in my other logs to but for longer periods of time I think it might be happening when I reset the iac position on the scanner. I will run another log today without resetting to see if it happens again.

Injuneer

If I had to guess, I'd say the file you started with, before you converted it to a .jpg in Paint, was a .csv file. That is the common output for some scanning programs, including Scan9495.

Upload the original file to an FTP site, and post the address here, or just send me the file.

The 3188 RPM target idle speed has already been pointed out. I have to look at some old data logs, because I think when the ignition is turned off, the target idle will show up at a value similar to that. [EDIT]Checked, that is exactly the number that appears in the target RPM column when the ignition volts go to "0". [EDIT] Possibly the system lost power or a ground for a fraction of a second. It also appears that in that frame of data, the A/C pressure and temp start to drop. And, engine RPM has dropped 145 RPM in the same frame that has the 3188 target RPM. The IAC is opening in response to the sudden loss of RPM. Then slowly starts to close as the RPM overshoots the target.

Do you get the sense that the engine is cutting off for a fraction of a second? Does the loss of RPM result from the A/C cycling?

Injuneer

PS: You need to provide the basic info about your car . Add a "Signature" with year, model, engine, trans and any major modifications.

Zee man

Ok, Ill do that. When I use the scanner to reset the IAC position it does feel like its shut off for a split second. And I see 3188 when I know its off so, that's a good call. When it is acting up, and I have had it on the scanner. The only thing I notice changing are the IAC numbers. Everything else looks normal. The IAC numbers go from around 10, all the way to 80 or higher. When its acting up. That is why I asked what the numbers correlate to. If nothing else changes why is the computer comanding such a drastic change in the IAC position? Everything was fine on the way to work today. Ill try it again on the way home.