EFI University

[Philo]

I've been chasing a problem with the ICV for a long time and can't seem to nail the problem. Here's what's happening.

When parked, If I slightly rev the engine above the target idle speed but below the low RPM reset position the idle position starts counting down towards zero. Then, if I let my foot off the gas suddenly the idle droops to about 400 rpm, some times lower causing a stall, and then the ICV starts to open back up to recover the low idle.

I've been told that the GM ICV used for the Tec3 6/12 is to be used with a 0v - 5v TPS and that the Tec does not require a TPS idle switch. One would think that if the idle switch was utilized the Tec would know the difference between a true closed throttle high idle and a low rpm/above idle cruise scenario, like when in stop and go traffic. Creeping along at 1200 rpm.

Here's my file running 4.9 software. Any suggestions are appreciated.

http://phil.files.infostreet.com/Tec3/Aug31st.WT4T3

Thanks !

Phil.

[RootesRacer]

I'm no expert on Electromotive ECUs, but most ECUs with closed loop idle control have a mechanism to disable closed loop idle control when the TPS is greater than a particular value.

Now if you opened the throttle a bit to get the revs to increase, and if the ECU has not disabled closed loop idle control, it would naturally close the IAC to compensate for the error.

After you close the throttle to its natural throttle stop, the IAC will now be more closed than it should have been.


Now I am of the opinion that IACs really should not be allowed to reduce speed, or should not be allowed much authority to reduce speed.
I usually set curb "hot" idle speed with the IAC closed, so the IAC can increase idle speed, but not decrease it.

[ETM]

Try changing IdleSpeed/IdleAdvance/Adv If Low from 0 to 3.

[Philo]

Holly short post batman !

I'm not a professional tuner so not quite clear on what you are asking me to try. Is your reply three separate suggestions separate by slashes "/", or one thought and suggestion.

"Try changing idle speed"
The factory idle speed recommendation for my engine is 925 rpms. So are you suggesting I go higher or lower? Also, how will this help with the dipping idle problem? The problem I see is that the Tec's IAC counts down to almost zero when the engine speed is raised above the idle speed but below the reset point. Then if I lift the throttle, the IAC can't recover fast enough.


"IdleAdvance"
Are you referring to changing idle advance where the engine idles on the Ignition Advance Table ? Or the idle advance for the IAC, low/high rpm advance/retard ? I have 10 degrees advance in the Ignition table for the idle areas. So can't I simply add 13 degrees advance to the cells below the idle target ?

"Idle if low from 0 to 3"
I think you're saying to set the IAC advance to 3. Note, I tried this once before and found that the rpm and advance oscillates when I raise the engine speed slowly with the pedal. This caused really bad drivability issues.

[ETM]

Sorry if it was not clear.

IdleSpeed/IdleAdvance/Adv If Low from 0 to 3.

Idle Speed Menu
Idle Advance Sub-Menu
Adv If Low value is currently 0, try a higher value like 3.

It should not cause oscillation at tip-in but Adv If High could. Maybe that is what you experienced before. Still, all the idle values tend to interact so it is entirely possible that this change will help the motor catch the idle droop but you will have to make changes to your sensitivities on the main screen to dampen things because it helps too much. Also don't get stuck on my 3 number. 1 or 2 degrees may be enough. Try them all.