What should idle RPM be?

[snidehockey]

mine usually hangs at 1100...is that normal? Seems high to me...I know that I have a sucky IAC valve cause idle is always weak when I take it out of gear and coast or brake...I have cleaned it multiple times though so I'm just wondering if it is what's making me idle possibly high.

I also can usually see grayish white steamish smoke out the pipes at night when theres a cars headlights behind me at a stoplight or something...running rich or burning oil? (it looks like when it's cold out and you first start a car...but this is Florida - ain't cold)

 

[CobraRed_96_GT]

regular idle should be around 550-600 or so when warm (if i remember right). Are you talking about when it's a cold start?

 

[lvmustanggt]

regular idle is 720

 

[CobraRed_96_GT]

regular idle is 720

hmm, tach might be off foe me then. Oh, that's right - most of the time it's not even working; damn ford tachs spin around an rarely come back.

 

[2000fordstanggt]

did you just reset your ecu? aka unplugging the battery. it usually takes awhile.

 

[[BlackDiamond]]

Make sure your AC / Defrost is off, see if that changes anything.

 

[2000fordstanggt]

Make sure your AC / Defrost is off, see if that changes anything.

yep, the compressor will definitly kick the idle up

 

[snidehockey]

nope it has always been that high...never been lower

 

[mustangkid05]

mine is around 7-750

 

[nyuk98gt]

snidehockey:

I can give you some hard numbers from my trusty SCT tuning program: stock idle in neutral is 656 RPM, and 565 RPM in drive. The manual cars should idle around 565 RPM or so. Now, there are modifiers to these base idle speeds (e.g.--a little more engine speed is added if the coolant temperature is colder than the normal operating temperature) so idle speed can vary a little. The idle is upped when more load is anticipated (like A/C), as the other guys said.

If you have access to a datalogger, you can confirm the true engine speed. 1100 RPM is too high for a stock/non-cammed engine.

Check your engine coolant temperature (ECT) sensor. If it is not working, the idle will be wrong and can be rough, too. Actually, a bad ECT sensor can have a bunch of bad effects.

HTH,

Chris

 

[steveb24]

I run 900 w/ the cams. idles smooth. i would do like 700 w/ the cams to get a nasty sounding lope, but it shakes the car too much

 

[SADL-UP]

I run 900 w/ the cams. idles smooth. i would do like 700 w/ the cams to get a nasty sounding lope, but it shakes the car too much

+1

 

[01BlkGT]

Check the bolt for your tb stop. It could be out of adjustment causing the higher than normal idle.

 

[snidehockey]

Man I'll tell ya what...I don't think I've ever seen my rpms below 800 let alone 565! If they got that low I have a feeling it would die out...

My problem is that whoever had this before me did ALOT of stuff to it that I keep gradually finding out the longer I have it (LT Headers, BBK O/R H, etc...) so I'm wondering if they had it tuned and raised the idle out of preference or to hide something.

There's a Steeda sticker on my radiator cover that I'm trying to figure what it's there for (what it came w/)...I doubt it's for looks - if they did underdrive pulleys would that require a higher idle to make up for less travel?

 

[96GTstang46]

Thats a REALLY clean motor buddy!!!

 

[nyuk98gt]

snidehockey:

Ah-ha! It helps to see the mods listed. The u/d pulleys will not affect idle speed. The LT's require more time for the O2 sensors to warm up (and it is sometimes difficult to keep them warm) so the idle quality can suffer. Like you said, the previous owner may have had Steeda provide a performance tune, maybe with a high idle to help keep the O2 sensors happy at idle (not the way I would do it but it will work). If the PCM was flashed with a new tune, there's no way to tell (that I know of, maybe the Ford techs can read the existing tune with that fancy Star NGS handheld device?). Maybe you can contact the previous owner and ask if he had a tune flashed in. It's worth a phone call, imo.

Anyway, you might consider getting yourself a dyno tune or performance tune [from a reputable tuner] so you can make adjustments to idle and other things yourself. There are plenty of options. FWIW, being able to tweak the tune is, to me, a huge part of the fun of adding mods. Tuning cars now is all through the computer (for the most part) unlike when I was a kid (and dinosaurs roamed the earth).

That's a nice, clean ride you've got there. Black Mustangs rule! Keep up the good work.

Chris