P1504

[joserw]

Hey all,

Here is my problem. I had an Accufab 70mm TB that I had sent back for readjustment. When I got it back and put it onto the car, the car threw a P1504 code (IAC problem/high idle). The car idles right around 1000 RPM. Also, the car did not throw this code with the stock TB on. I should also mention I have an aftermarket Standard brand IAC on the car.

I am just wonder if the IAC is the problem or if the TB needs adjusting and if so, could this be done by me in the driveway. Thanks.

 

[wmburns]

How to trouble shoot idle problems (IAC)

Likely the TB idle set screw is set too high allowing too much air to enter. Remember that the IAC can only ADD air (never remove it).

The DTC is thrown when the PCM sets the IAC duty percentage to zero and still can not slow the idle down.

This problem could also be caused by a vacuum leak after the TB butterfly.

Read post # 3

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

 

[joserw]

The idle set screw is the tiny screw that rests along side the TB arm correct? So just adjust that to let less air in and hope for the best.

Couldn't find any vaccum leaks.

 

[nyuk98gt]

joserw:

Once you have confirmed that there are no vacuum leaks then you can set the throttle body stop screw.

The correct method of setting it is to:

a) loosen the lock nut;
b) tighten the screw until you see some gap;
c) reduce the gap to 0.010";
d) reduce the gap by exactly one (1.000) turn;
e) tighten the lock nut (while holding the screw in position).

The PCM relearns the closed throttle position at every start-up. Setting the stop screw (as above) will put the amount of air getting by the closed blade at or near stock. There is a value in the tune that can be adjusted but that is not necessary (and you would need access to the tune).

This should do the trick.

HTH,

Chris

 

[Ponyup1]

Idle Air Control Circuit Malfunction.
Your throttle body stop screw needs to be adjusted correctly.
Yes also check for the presents of a vacuum leak.

 

[joserw]

It is an Accufab TB so there is no lock nut, just a screw with an allen key head. How should I adjust this?

 

[wmburns]

That's it. Adjust in small increments.

Back out (CCW) the screw to close the TB (less air).

Note, it will take time for the PCM to re-learn the new idle trim. You must close the set screw more than what it takes to get the idle into normal range. Otherwise, the idle may still be too high depending upon the weather.

Just confirming that there are not vacuum leaks. It is not possible to adjust out a vacuum leak.

 

[joserw]

I'll be adjusting it to close it (screwing it counter clockwise) correct? So I am letting less air in.