Idle speed question

[nitrofarm]

Hey guys why does the book say to ground the sti link when you adjst idle speed? Cant you do it on the fly by feel? This is on my Aspire btw...I know when you set timing they want you to grd it to get rid of any advance right? But why when adjst idle speed? Thx

[georgeb]

My guess is that the computer knows that you are changing something and not throw a code. I've piddled with mine without doing that with no problems.

[FestYboy]

^ nope! the base idle is mechanical and is not controled or monitored by the ECM. base idle adjustments should be done with the engine at operating temp. if the engine isn;t up to temp, the IAC is still active and controling the idle, so any adjustment of the base idle screw will be fighting the IAC. the IAC goes offline once the engine is up to temp.

[avitsef]

^^
Smart Guy .... good info , thanks .

[kartracer46]

^yeppers he is!

[georgeb]

^ nope! the base idle is mechanical and is not controled or monitored by the ECM. base idle adjustments should be done with the engine at operating temp. if the engine isn;t up to temp, the IAC is still active and controling the idle, so any adjustment of the base idle screw will be fighting the IAC. the IAC goes offline once the engine is up to temp.

So what does grounding the plug do?

[avitsef]

Uh hu from what ive read from him ... so where does the IAC get its info from ? Sensor in the head ? Just learning here !

[FestYboy]

^ IAC is a stepper motor that controls a pintle valve based on ECU input from the ECT, VAF and dizzy (rpm input). the pintle valve closes once the coolent reaches close to operating temp and the airbleed screw on the TB takes over for base idle speed.

George, the grounding plug is there to lock out the electronic spark timing control ONLY. base idle speed AND base timing must be adjusted in tandum to get correct base tuning.

[georgeb]

So is it okay to tweak the idle without grounding the plug?

[kartracer46]

^and there you have it folks!

[avitsef]

[QUOTE=FestYboy;489879]^ IAC is a stepper motor that controls a pintle valve based on ECU input from the ECT, VAF and dizzy (rpm input). the pintle valve closes once the coolent reaches close to operating temp and the airbleed screw on the TB takes over for base idle speed.

Wow ! Thanks , had to read that about 5 times before 1/2 of it sunk in .

[iceracerdude]

The book says to ground out for idle or timing.

[nitrofarm]

^ nope! the base idle is mechanical and is not controled or monitored by the ECM. base idle adjustments should be done with the engine at operating temp. if the engine isn;t up to temp, the IAC is still active and controling the idle, so any adjustment of the base idle screw will be fighting the IAC. the IAC goes offline once the engine is up to temp.

Thanks FestY-this all make sense now. During my process I witnessed what I know believe was the IAC "dropping of line". And my first thought was. "Great now I got something wrong with my Dizzy". Because it was a noticable sound change in the idle. Almost like you put your hand over the inlet of the intake air tube.
All that said I'll let it warm up more before I start the process. Prolly till the cooling fan cycles once. Then I'll ground the sti & set the idle speed.Bottom line.I must not have let it warm up enough. Thanks all for good feedback!