Another hanging idle question?

[Addermk2]

that IS wrong, the reason being is that the ECM is programmed to know that at X rpm, with the throttle closed, there should be Y amount of airflow. These f=values can be seen in the TB Airflow scalar, the neutral idle scalar, and the TPS breakpoint.

basically, the surging you get, or the hanging idle... is from the car being at a high rpm, the ECM says "the IAC is open to this much, and the throttle is closed.... so then why am I at this high an RPM?" and closes the IAC valve to bring the car down to the PROGRAMMED idle RPM. so now your idle drops off, typically falls below the programmed RPM and the ECM goes "holy shit, im going to stall!" flips the IAC open again, and your RPM shoots back up.

thus creating idle surge.

NOT setting your base idle to the RPM programmed into the ECM... WILL and i repeat WILL cause rpm hang. Ive seen it and corrected it on more than one vehicle. My own included!

As for cam selection causing idle problems in SN-95's... bullshit.
My cam is .579/.579 lift 236/245? duration @ .050, and has a 110? LSA. With no tune what so ever in my car... just the basic built in maf transfer function that is already in the eec analyzer software... my car idled smooth as silk at 750rpm. So i say, if you cant get your E-cam, F-cam, shit-cam.. whatever cam, to idle smooth. Its not the hardware... its the person working on it.

Keep in mind that there are many factors that affect the way your car idles. Vac leaks, fuel pressure, timing (i still see people running stupid amounts of timing.... its not getting them anything DONT GO PAST 12? FFS!), oxygen sensors, IAC motor cleanliness, EGR function. So if you REALLY cant get your car to idle the way it should... look into these things. I bet you will find one of them ultimately to be the culprit.

 

[95-stang]

"basically, the surging you get, or the hanging idle... is from the car being at a high rpm, the ECM says "the IAC is open to this much, and the throttle is closed.... so then why am I at this high an RPM?" and closes the IAC valve to bring the car down to the PROGRAMMED idle RPM. so now your idle drops off, typically falls below the programmed RPM and the ECM goes "holy SH*T, im going to stall!" flips the IAC open again, and your RPM shoots back up. "

Well that does make some sense.

While i'm on the subject where should the air screw on the throttle body be set?
I've read about 2 turns out, 1+ half etc etc.

 

[Addermk2]

While i'm on the subject where should the air screw on the throttle body be set?
I've read about 2 turns out, 1+ half etc etc.

air screw? Are you referring the the throttle stop screw...? I dont recall any other possible place that you could be referencing.

 

[95-stang]

Sorry, you refer to it as the ISC bleed screw, which is usually about 1.5 turns out on a stock throttle body, but most of us are not using stock.

 

[Addermk2]

I never touched i when I had the stock TB. since nothing about it had changed, there was no need to dick with it.

 

[95-stang]

Well i dont have a stock throttle body same as a lot of others, so how do you know the bleed screw is set correctly?

 

[Addermk2]

i still dont know what screw it is you are talking about. so I cannot comment on it

 

[95-stang]

Have a look on any throttle body, on your stocker its under the rubber plug, on my BBK for instance its a fairly large brass screw on the opposite side to the throttle stop screw.

http://www.summitracing.com/parts/BBK-1522/?rtype=10

Enlarge that pic and its on the left hand side.