Can someone PLEASE describe to me the EXACT symptoms experienced by this so-called "idle stumble" when the AC is on???

Here is what happens with my car:

Engine idles at 800 RPMs with the A/C OFF. Needle is steady. No issues.
I hit the AC Button, and the needle jumps up to 900 RPMs and stays there at idle.
I turn the AC Button OFF, and the needle returns to 800 RPM's...


Is This what you guys are talking about?

Here is what I don't get. I dont quite understand this because I've been running 4 different intake configurations and I get the very same results on ALL INCLUDING the STOCK AIRBOX with STOCK AIR PANEL.

Please discuss!

 

The problem in the discussion of the A/C fan and the stumbling is when you add the open element filter to the car you of course remove the air box. This leaves the filter out in the open.

When the A/C is turned on and runs for while the A/C fan comes on to help with the cooling of the car. When that fan comes on it blows air directly into the filter. This causes the mass air flow sensor to read crazy because its not just sucking air in but more air is being forced into the the system because of the fan. This in return messes up the mass air flow reading and the car doesnt quite know what to do.

When you block off that side of the filter the problem goes away because the air cant go straight into the filter and the car goes back to sucking in the normal amount that its used to.

The RPM's jump and fall when this happens. It just doesnt stay at 900rpm. I would say what you're experiencing is the stock ECU raising the revs to compensate for something else running that draws power such as the A/C.

I wouldnt say you have a problem i would say thats the nature of what its supposed to do.

 

thanks for the clarification Jarrod. Im just a bit confused because I am not experiencing erratic idling with the fan... and this is with a $40 cone, the nisei-prototype intake, the stock airbox and filter, and the ARC induction box....

I'm just curious what the actual description is of this idle-stumble is since I think some people on the forum might be describing what is otherwise "normal" as an idle issue and confusing the two...

 

You're welcome.

The stumble with the mass air flow sensor due to the A/C issue is as I mentioned in the first post of the RPM's dropping and raising quite significantly due to the mass air flow sensor trying to recalibrate itself due to the extra air being forced into the system.

To add to my original post as I tried to keep it brief.... the a/c fan problem is also due to the increase in air temperature that the mass air flow sensor is seeing. When that cooling fan kicks on it is blowing all of the hot air off of the radiator into the intake as well so that will in turn just add to the problem. While there is more air going in its also trying to calibrate for the increase in air temperature.

As I said all you're experiencing is the ECU compensating for drawing more power from the car's electrical system. In order to keep up with the extra draw of power the ECU is raising the RPM's so the system is not overdrawn on power. You can also see the RPM's move when you do the heat, headlights, etc... its just the nature. Its normal. Nothing to worry about.


I hope this clears things up a little for everyone. Im glad to help out!