Idle problem and car stalling

east_sidaz · Sep 18, 2010

Hi,

My 99 GT stalls when i come to a stop and it idles bad sometimes. When i'm at a stop and hit the gas a bit the rpm will go down to about 500 and car wants to stall. And sometimes does. I thought it might be from the IAC, so i pulled it and turns out it is new because previous owner had replaced it a few weeks ago. There is a black knob on top of the IAC which i didnt know what its for. Could that be the problem? that i need to adjust that?
See pics below

Note how clean it is :

Any thoughts ?

wmburns · Sep 18, 2010

How to trouble shoot IAC idle problems

The black knob on the IAC is a vent. It is used to allow air to start the motor.

Clean the MAF. Use only products designed for the job. Never use harsh cleaners or cleaners that leave a residue. No brake clean. No carb and choke cleaner.

Check for vacuum leaks. All hoses, oil cap, dip stick, valve covers, in short any place unmetered air can enter. Even a small leak can cause problems.

For a slow idle the usual places to pay special attention to is the IAC bypass line and ignition.

If the ignition is weak, this can cause a slow idle. This can also casue driveability issues. Check plugs, wires, COP's, coil packs.

Excessive EGR flow can also cause stumbling and other power loss issues.

Finally review post 3

http://www.stangnet.com/mustang-forums/810729-starts-but-dies-idle-help.html

east_sidaz · Sep 18, 2010

Yah i will do that. Regarding cleaning the MAF, i know i should use either carb cleaner or MAF cleaner. I might not have access to those. Is it ok to use WD40? i wont be able to source MAF cleaner, any thoughts?

castine917 · Sep 18, 2010

maf cleaner can be bought at many parts stores. why can't you source it? wd40 is a lube not a cleaner and could cause more problems.

wmburns · Sep 18, 2010

east_sidaz said:
Yah i will do that. Regarding cleaning the MAF, i know i should use either carb cleaner or MAF cleaner. I might not have access to those. Is it ok to use WD40? i wont be able to source MAF cleaner, any thoughts?

use WD40 or carb and choke cleaner if you want to ensure there will be additional problems.

The MAF is a very delicate sensor. Cleaners that are HARSH or leave any RESIDUE will permenantly damage the sensor. Hence the specific warning to use only cleaners designed for the job.

OBTW, use of a cleaner like WD40 is almost guaranteed to ruin it. The oil residue will alter the calibration thus rendering it worse than usless because it will forever report an incorrect air flow.

Any cleaner used must not leave even the smallest amount of residue.

Brake cleaner is too harsh for the job.

nickmckinney · Sep 18, 2010

Is this a cammed car?

east_sidaz · Sep 18, 2010

nickmckinney said:
Is this a cammed car?

Ok good point.
First let me say this. I just finished checking everything. MAF is ok. IAC ok also. No leaks or bad hoses.
I recently installed MHS Stage 1 Heads & stage 1 cams. This all started after that. The car hasnt been tuned yet, as there are no local tuners and a mail order tune is my best bet. But i didnt think that stage 1 cams will cause idle problems. comments?

wmburns · Sep 18, 2010

I think that was critically important fact to have mentioned in the opening post.

Let's see. Big cam, no tune, problem started right after the cam install.....

OBTW, A big cam can lower engine vacuum. The black vent on the IAC needs a pressure differental in order to close. If not enough pressure differential, the vent may open and allow unmetered air. The unmetered air causes the MAF to under state the air and the motor goes LEAN.

However, this is almost surely a tune issue needing an updated load table.

east_sidaz · Sep 18, 2010

wmburns said:
I think that was critically important fact to have mentioned in the opening post.

Let's see. Big cam, no tune, problem started right after the cam install.....

OBTW, A big cam can lower engine vacuum. The black vent on the IAC needs a pressure differental in order to close. If not enough pressure differential, the vent may open and allow unmetered air. The unmetered air causes the MAF to under state the air and the motor goes LEAN.

However, this is almost surely a tune issue needing an updated load table.

Well i never thought stage 1 cams require a tune. Even the VT stage 1 cams didnt require a tune, unless you go with stage 2 !!
Anyways, u might be right though that the reason for my idle issue is running the factory tune with stage 1 cams & heads.
The black knob on the IAC can be turned right and left, and i didnt really know what to do with it, because my 2004 GT didnt have that knob, so i just left it like that because it didnt really matter which way i turned it. I do have a Diablo hand held tuner, so i would need to get a mail order tune. Does anyone know where i can get a mail order tune? I asked Diablo but they dont do mail order, so!!?

wmburns · Sep 18, 2010

The black knob is not an adjstment. Turning it does nothing.

When you go to the Doctor for check up, don't you mention everything wrong or would you fail to mention that you are having chest pains?

There a reason that the list is mods is important to this process.

I initially said to myself I was not going to answer anymore posts from this thread. However I guess I can't help myself.....

You have an ODB2 tuner. You have the power to answer all of these questions for yourself.

At normal engine temperature Data log RPM's, MAF, load, TPS, LTFT bank 1/2, IAC duty cycle, EGR flow, and fuel pressure during idle and slowly increasing RPM's. Graph it.

The answer will be right there in the graph.

What is not fully appreciated is now armed with the knowledge that major work was done just before the problem stated, this brings into question items not normally considered.

Are you positive the motor is correctly timed? What is the result of a compression test? What is the engine vacuum at idle and under load? Is the fuel pressure sensor vacuum reference line connected?

nickmckinney · Sep 18, 2010

Yup its the cams, raise your idle speed as high as you can deal with and tweek the IAC values.

If a cam doesn't need a retune its a cam not worth buying.....................

Idle problem and car stalling

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