Still having a minor idle issue on the '04

[Mr. Man]

I replaced the IAC and that fixed part of the issue, but now the car idles up high for a few seconds longer than what seems normal(compared to the '03) then suddenly drops down. Does this warm or cold. No codes or idiot lites. Car accelerates fine and shifts OK so I'm not sure the TPS is on the fritz. Any ideas would be helpful. :)

[Mr. Man]

Just got back from a long cruise and I have some symptoms that may help narrow down the issue. Cars runs OK at speed and when I put my foot into it it reacts like a scalded dog( Thanks Mo's). I did note though upon braking the idle would come down as one would expect with the engine slowing, but when I would release the brake pedal the idle would shoot up a few hundred RPMS, hang, then drop down. I also noted the idle RPM is about 8-900 instead of the 650-700 that I think is normal.
There also seems to be a dull zone for lack of a better term when coasting. It feels like when the car is slowing due to the engine( no throttle) it suddenly releases and the RPM raises. Similar to the example I gave above, but occurs at normal driving speed.
If you have specific questions I'll do my best to answer them as intelligently as I can.

[Pat]

Does it seem there is a correlation between what the transmission/torque converter is doing and the engine? At steady speeds, the car is fine, but slowing or speeding up (shifting) the problem is manifested, if I understand you correctly.

Is it too much to ask that a tranny professional test it out?

[Turbov6Bryan]

Look for vacuum leaks

[justbob]

FYI the two bolts for the IAC only need to be snug. Someone on here a few years back had repeated issues with their IAC and it ended up being so tight that it caused a slight vacuum leak.

You do have big hands.. [emoji1303]


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[Mr. Man]

Look for vacuum leaks
Will do. Are there any vacuum lines under the car/motor?

[Mr. Man]

FYI the two bolts for the IAC only need to be snug. Someone on here a few years back had repeated issues with their IAC and it ended up being so tight that it caused a slight vacuum leak.

You do have big hands.. [emoji1303]


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I bought a new gasket with the new IAC and snugged tight with a nut driver. I don't think it's to tight. I tried to match the effort it took me to break it free.
I did finally break down a buy a new PCV/gasket and am waiting on a new PS PCV tube. The old one is quite greasy.
Going to look for all the vacuum tubes I can find as suggested. Does a vacuum leak make sound? I don't hear any unusual noises under the hood, but if a vacuum leak makes faint noises I may need to listen harder.

[Zack]

Are you starting your car with the AC on?

[Marauderjack]

Are you starting your car with the AC on?

I have always started with AC on......is it wrong Zack???:confused:

[Mr. Man]

Are you starting your car with the AC on?
No. I try and make a point of turning it off as I approach the driveway.

[Mr. Man]

I have always started with AC on......is it wrong Zack???:confused:
It can put an extra load on the engine.
I think Zack may have been thinking the compressor switching on and off may be the cause of the idle mystery. I read about that while reading possible reasons in a google search.

[Mike M]

Also check the minimum idle speed with the IAC disconnected. If its at all too high it can cause this as the IAC with will get confused.

[1stMerc]

When you replaced the iac, how long did you let it sit at idle before you drove it? Read somewhere you should let it sit at idle for two minutes or so then turn on the lights or something to put a load on the motor before driving off. Works for me every time I change my tune.

[RF Overlord]

Does a vacuum leak make sound? I don't hear any unusual noises under the hood, but if a vacuum leak makes faint noises I may need to listen harder.Vacuum leaks can be very hard to localize by ear. Gently spray a little MAF cleaner or similar around the suspected areas. If the idle suddenly changes, you've found it.

[Mr. Man]

Also check the minimum idle speed with the IAC disconnected. If its at all too high it can cause this as the IAC with will get confused.
If I recall correctly when I replaced the IAC I tried disconnecting it and the engine surged and died. Based on what I read on Google(which never lies) that is what was supposed to happen if the IAC was working correctly.

[Zack]

This can be adjusted via the idle air adder at startup. Fyi

[Blackened300a]

Just got back from a long cruise and I have some symptoms that may help narrow down the issue. Cars runs OK at speed and when I put my foot into it it reacts like a scalded dog( Thanks Mo's). I did note though upon braking the idle would come down as one would expect with the engine slowing, but when I would release the brake pedal the idle would shoot up a few hundred RPMS, hang, then drop down. I also noted the idle RPM is about 8-900 instead of the 650-700 that I think is normal.
There also seems to be a dull zone for lack of a better term when coasting. It feels like when the car is slowing due to the engine( no throttle) it suddenly releases and the RPM raises. Similar to the example I gave above, but occurs at normal driving speed.
If you have specific questions I'll do my best to answer them as intelligently as I can.

Your "in-drive" idle is set too high, normal is around 600-650, also I'm having the same issue with idle surge coming to a stop, the idle would drop out, then raise and drop out again repeatedly, Its the TC lockup in the tune that making it do that. I tried having my tuner correct it, but I gave up after several reflashes and a new IAC. I even datalogged my car and he found nothing wrong in the tune so I just learned to live with it until I decide to get the car re-tuned or let him drive it to see what I'm talking about.

Here's a example of what its doing.
A8SaVyLUXgI

[RubberCtyRauder]

Your "in-drive" idle is set too high, normal is around 600-650, also I'm having the same issue with idle surge coming to a stop, the idle would drop out, then raise and drop out again repeatedly, Its the TC lockup in the tune that making it do that. I tried having my tuner correct it, but I gave up after several reflashes and a new IAC. I even datalogged my car and he found nothing wrong in the tune so I just learned to live with it until I decide to get the car re-tuned or let him drive it to see what I'm talking about.

Here's a example of what its doing.
A8SaVyLUXgI

I have the same issue..coasting at about 2000 rpm, then dips to 1500, back to 2000 and repeats..I hate it.. It must not be visible in the tune as I too have had tuner adjust IAC for it originally, but it hasn't seem to change anything. I too would like a fix for it.

[justbob]

Your "in-drive" idle is set too high, normal is around 600-650, also I'm having the same issue with idle surge coming to a stop, the idle would drop out, then raise and drop out again repeatedly, Its the TC lockup in the tune that making it do that. I tried having my tuner correct it, but I gave up after several reflashes and a new IAC. I even datalogged my car and he found nothing wrong in the tune so I just learned to live with it until I decide to get the car re-tuned or let him drive it to see what I'm talking about.

Here's a example of what its doing.
A8SaVyLUXgI

I've learned to deal with hanging idle until fully stopped for one second and horrible bucking trying to maintain speed at 25-30. It sucks..

The thing with Eric's case is he hasn't changed his tune.


I have the same issue..coasting at about 2000 rpm, then dips to 1500, back to 2000 and repeats..I hate it.. It must not be visible in the tune as I too have had tuner adjust IAC for it originally, but it hasn't seem to change anything. I too would like a fix for it.


Like I mentioned above, I've had IAC issues for over three years now with different tuners. I've been through two known good IAC's and one new Motorcraft one with zero changes. All mine stem from switching over to a manual trans with all auto functions alive in one and all off in the other tunes and nothing changes. All diagnostics are in check and all known values adjusted accordingly. I've just learned to live with it amongst other issues.

Another reason why I'd feel quilty if I sold it. Some small inconveniences I've learned to live with or adjusted my driving technique for. I couldn't possibly remember all and after I'm done rambling about the known ones I'd feel like I was selling a beater..


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[Mr. Man]

The SB is doing just what Blackeneds video shows. The only thing I have done is replace the IAC with a new Motorcraft one. The car does this weird surge with both the OEM and Mo's tune. It didn't do it last year with either tune. Still hunting down a possible vacuum leak but nothing is glaringly obvious. Still waiting on a new PCV tube for the PS which I hope comes in this week. There is a lot of oily reside on the present tube so I'm thinking there maybe a leak here. Inch by inch row by row.:)

[Marauderjack]

Try disconnecting the negative battery lead for a few minutes to reset the Adaptive Learning........this would fix mine when I had the Diablo Tune in it!!:beer:

[Mr. Man]

Try disconnecting the negative battery lead for a few minutes to reset the Adaptive Learning........this would fix mine when I had the Diablo Tune in it!!:beer:
Couldn't hurt.

[Pat]

Mr Man;

one of my vacuum lines rotted through and caused idle problems for me yesterday. See my thread today "what line is this" for a picture. Check yours.

[Mr. Man]

Mr Man;

one of my vacuum lines rotted through and caused idle problems for me yesterday. See my thread today "what line is this" for a picture. Check yours.
I've been waiting on a new PCV hose for a bit. Dealer ordered the DS by mistake.