Idle too low, how do I get it up??

[crawlin60]

seriously, I'm idling at 600 in drive and would like it to be closer to 650-800. Just installed a new alt, cleaned ISC valve, (idle is glassy smooth) new cables (ouch$$) and batt terminals, battery as well. Didn't want to hijack RandyS' ISC thread. I hear of an airbleed that does that, anyone else heard of that?

 

[GXO]

The intake rubber can crack and cause idle issues...vacuum problems can too.

Start there as they are free to find and cheaper to fix.

 

[tomlite]

Not to make your persuit seem imposible, but the idle speed is set by the engine control computer. It will alter ICV, timing and Fuel delivery to achieve the target RPM.

 

[GXO]

which is why something impacting the system will impact the idle.

vacuum leaks are the culprit usually.

 

[robbie]

600 in drive is the idle for the computer to shoot for. If you want more you will not get it unless you manually over ride the throttle plate with a hand throttle or a electric step motor. You may need to varify the idle with a timing light with a RPM counter. The only other time it may idle higher is with the A/C on, Idle is then trageted for around 800 with the elcetric clutch for the AC is on. So if you try to set a different Idle the computer will keep readjusting it back to 600 as long as the TPS is reading the throttle in the idle position. later robbie

 

[xl715]

If it's idle is lower than it used to be, it could be due to all your work. I've noticed after messing with stuff and having the battery disconected it takes a while to re learn the idle and will seem to idle low for a little while. It relearns and corrects it self with out having to do anything special.
If it's always idled at this rpm and you just want it higher I agree with robbie!!

 

[chacoetaco]

I've noticed after messing with stuff and having the battery disconected it takes a while to re learn the idle and will seem to idle low for a little while. It relearns and corrects it self with out having to do anything special.

Yep, me too.

 

[landtank]

I've driven about 4000 miles since the HG replacement. Before the work I was erratic but mostly at about 650 rpm in drive. I'm now a rock solid 600 all the time. Glad this came up as I thought I might have screwed up something.

 

[crawlin60]

I was afraid of that answer (ECU set idle speed). I'll chase a different lead then then, cause I'm afraid I haven't replaced the last alt with this one that went in yesterday.
Thanks

 

[Scamper]

Ben,

As others here have noted, you may just be chasing your tail on this. An idle of 600 rpm that you report is smooth as glass does not sound like a problem. Mine idles at 600-650 and I belive that's within spec.

I'm more inclined to think your previously higher idle was due to a sticky cable or dirty TB, etc that you've apparently fixed. You should probably be thankful--most of the guys here are trying to get their trucks to run like yours!