Idle Speed?

When I flashed my initial tune from Lund, I noticed the car idled noticeably higher. I asked, and they sent me a revision for a stock idle. Car now idles as low as 620-630 sometimes, but at other times still idles around 740. Running the AC compressor does seem to make it idle higher, but not always. Sometimes it will be around 630 with the AC running. I thought maybe it has to do with load demanded from the charging system but radio and e-fans don't seem to have any effect. This is probably something I've only noticed since ive been aware. Never really paid that much attention on the stock tune. Can anyone tell me what the idle characteristics are on a stock car? And should the AC have a noticeable (100 rpm) impact on idle speed?

edit..... just to be clear I never get a hunting or surging idle....I just don't know where the idle will settle at. Sometimes 630ish and sometimes 740ish
Thanks

you asked for a lower idle.

craigsix said:

you asked for a lower idle.

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Yes...but it doesn't always idle lower. Only trend I can detect is that it idles higher when it's hot.

for anyone following this...ive got some real issues now. See thread below:

http://www.mustang6g.com/forums/showthread.php?t=87044

Just loaded my Lund tune and noticed the higher idle as well. What's the reasoning behind this? To Help with oiling?

I couldn't get them to tell me. I'm still curious what "stock" idle speed is supposed to be.

ManBearPig said:

I couldn't get them to tell me. I'm still curious what "stock" idle speed is supposed to be.

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I think it's about 680 RPM but I could be wrong :shrug:

My idle speed is pretty crazy too and I'm stock (other than full suspension and corsa sport) and I never noticed until I put an Airaid intake on, then I was convinced it made my car ideal all over the place so I took it off and sold it...then it idled the same way it did with the Airaid. Point being, maybe it's exactly the same you just didn't notice until you got a tune?

I just crank it up and drive now. I don't pay it any mind

It is most likely the same and I just never paid any attention before. There's also no real way to tell exactly what the speed is without a scanner or such...but I notice the car idles round 630 on the stock tune per my ngauge. And it idles at 630 on the Lund tune for the most part, but still randomly idles at 740 for no apparent reason. Stock tune doesn't do this. Just wondering if that's "normal" since I keep reading 680

Maybe it's because your A/C is on? Mine idles up and down and sounds like a "miss" with the a/c on

Saywhen said:

Maybe it's because your A/C is on? Mine idles up and down and sounds like a "miss" with the a/c on

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When the AC compressor cycles on/off the rpm hiccups for just a second then stabilizes. I know that's to be expected. . If the AC is off, car is idling at 630, and I turn the AC on....it will sometimes (but not always) increase the idle to 740 and remain there indefinitely.

ManBearPig said:

When the AC compressor cycles on/off the rpm hiccups for just a second then stabilizes. If the AC is off, car is idling at 630, and I turn the AC on....it will sometimes (but not always) increase the idle to 740 and remain there indefinitely. This is only with the tune, mind you. Stock tune it always idles at 630

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I know mine was pretty low stock. Now it's 750ish all the time no surging at all. Maybe your air temp sensor is missing the gasket? When I had my 03 cobra dyno tuned they (modular depot) raised the idle to about 750 also. I don't mind it since I feel it helps with oiling, maybe I'm wrong?

Mine also cycles up from 625-750rpm ever few seconds with the A/C on. Normally cars do that to prevent stalling when the a/c kicks on, then adjust and lowers idle. Perhaps my a/c refrigerant is low causing the issue but I haven't checked. When tuning the idle for a/c on and off are separate tunes. Never tuned mine. With the a/c off it idles 625-630 which I had lowered from 750 as well. Never given a reason why it was higher than stock, same issues as OP.

Its because of the VCT trying to balance stability and fuel consumption.

Base idle in gear is 645, in neutral its 650.
You then have a MAX idle based on coolant temp.
a table based on gear and coolant temp.
then you have minimum tables for neutral and drive/in gear vs VCT.

Watch your intake cam angle and you'll see it going from 0 up to 30. At 0 it will idle higher and be more stable(extra load from AC, alternator, gear engagement, ect.), at 30 it will idle lower and be more fuel efficient when it can.