idle and AC, read this

[sapper]

Many of you may not of noticed this, with all the warm weather so far, but this may be a problem to check out.
When the car is at idle with out any venting or AC turned on, the car has a rough idle. If you turn on the AC the RPM's will pick up a little and the car's idle will smooth out nicely.

Anyone have any information about this AC effect on the car's idle?
Anyone have any thing done to fix the rough idle?

Post here if you have the same effect that I have posted. I wonder if this is going to effect just a few of us or its a problem for everyone.

 

[2003snake]

ditto here

 

[JoeAsheville]

Sapper, I have read that someone found a set screw that they adjusted to bring up the car's idle. If you have owned 5 liters in the past, you would recognize the same concept on a 4.6. All it is, is an adjustable throttle stop that holds the throttle blade open a tad bit more.

When the A/C is turned on, if the new cars are *anything* like the old ones...a "dash pot" (servomotor/plunger) engages the throttle to raise the RPM back to a preset range, to counteract the increased operating load placed on the engine by the A/C compressor at idle.

If the dash pot raises the idle up into what the driver considers to be a "smooth" idle range, then this is consistent with your observation.

Recommendation: check the RPM that the car idles at with the A/C on, then attempt to duplicate that with the set screw with the A/C turned off.

Let us know how you get on.

 

[NickSVT03]

I have that problem too. Anyone hear a clunk noise when there ac is at idle every now and then too?

 

[agbulit]

i've noticed the same phenomenon.

 

[03DOHC]

Clunk noise every now and then should be the a/c clutch cycling. It's normal unless it cycles excessively.

 

[03SoCalCobra]

It also ups the timing when the AC is on- compensates for the AC load.

 

[1svtcobra]

Same here. When the car is cold it idles perfect. When it heats up it idles rough. Then I turn the A/C and it idles F____ing Perfect. Why didn`t Ford just make it idle like that all the time.

 

[mineral03]

I recall someone sayin they did that for fuel economy, keeping the idle as low as possible... Im not gonna spend any time on it, mine does it too, but i dont even notice it anymore, since iput the exhaust on, now hte whole car rumbles

 

[King Cobra 03]

same here, complained about it when i had it in for service, they said they did'nt notice anything.

 

[Cobra'03]

The reason the car idles better is the timing advance and the slight bump in RPM. The reason Ford didn't "do it in the first place" should be obvious - the EPA start and loop certification is done without the A/C on - if it were on, the emissions would be higher.