Erratic idle with A/C on

T3rminator · 06-10-2007, 12:11 AM

I suspect this might be more AU ECU related rather than T series specific.

I've noticed recently (last 3 weeks?) that when I drive with my A/C on the car idles erratically. When I pull up to a stop, the revs would bounce from say 500RPM to 1000RPM to 500RPM and so on. Sometimes it would just sit on 1000RPM which is quite high. Any ideas what is causing this?

I don't use the AC often but have only noticed it lately when I have had to clear the window due to fog caused by rain.

philstoj · 06-10-2007, 12:16 AM

Does it get better at all? i know mine does this, as i dont use the air con often, but after a bit of driving, the comp learns and it idles almost like normal.

**Stav** · 06-10-2007, 12:19 AM

The ac loads the engine and makes the idle speed drop .This is why the ecu is trying to make the car idle.It adjusts the idle speed controller up to keep the car idling. I would say clean the idle speed controller with a a cleaner.Remove the 2 allen key screws and clean it out.It may be carboned up. Failing that clean the throttle body by removing it and spraying a suitable solvent.Hope this helps

T3rminator · 06-10-2007, 12:32 AM

I usually just switch the AC on for a period of 2-3 minutes until the fog goes away...so I haven't gone for a long drive with the AC on to see if it settles down. Sometimes it idles fine...then goes cranky again at the next set of lights.

Where abouts is the idle controller?

I might do a reset tomorrow and see if that helps.

JC · 06-10-2007, 03:38 AM

Quote:

Originally Posted by T3rminator

I usually just switch the AC on for a period of 2-3 minutes until the fog goes away...so I haven't gone for a long drive with the AC on to see if it settles down. Sometimes it idles fine...then goes cranky again at the next set of lights.

Where abouts is the idle controller?

I might do a reset tomorrow and see if that helps.

A reset should work if you have an auto and follow the relearn procedure,; not sure how it works in a manual (it's not like you can let a manual idle in gear with handbrake on).

I would suspect ISC valve too - it sits on top of the Throttle body and has a big black electrical plug attached to it.

GK · 06-10-2007, 07:41 AM

This will help.

Cleaning ISC Valve
http://www.fordforums.com.au/showpos...9&postcount=43

Cheers,

GK

T3rminator · 06-10-2007, 10:01 AM

Hmmmmmmmmmmm think I found the culprit... I must have disconnected it when I was changing plugs. What does this thing do?

GK · 06-10-2007, 12:11 PM

Not sure but it's a sensor of some kind. Hooked up to intake piping so airflow or something or other!

Is it all good now you've plugged it back in?

GK

T3rminator · 06-10-2007, 12:14 PM

: Its all sweet now that I have replugged it. Idles perfectly.

And that plug is the IAT sensor. Found it in the Technical Resource section.

GK · 06-10-2007, 04:03 PM

Quote:

Originally Posted by T3rminator

: Its all sweet now that I have replugged it. Idles perfectly.

And that plug is the IAT sensor. Found it in the Technical Resource section.

What does IAT stand for?

Glad it's all sorted.

GK

JC · 06-10-2007, 04:08 PM

Intake Ait Temperature. The V8s use a MAF to sense air flow, and IAT to determine air temp. I6s use a MAP - Manifold Absolute Pressure - sensor which combines air flow and temp into one reading (pressure - being a factor of Volume and Temperature).

GK · 06-10-2007, 06:57 PM

Quote:

Originally Posted by JC

Intake Ait Temperature. The V8s use a MAF to sense air flow, and IAT to determine air temp. I6s use a MAP - Manifold Absolute Pressure - sensor which combines air flow and temp into one reading (pressure - being a factor of Volume and Temperature).

Another helpful service from JC's knowledge bank!

I'm glad you're still around mate!

GK

Burley · 07-10-2007, 02:44 PM

hey all sorry to take the thread but mine is doing the same....bought a working isc valve thanks to au3xr....cleaned it....doesnt do it all the time...but it idles fine just sometimes the revs stay up till i switch off a/c or touch the accel

T3rminator · 07-10-2007, 02:49 PM

If the idle isn't bouncing around then I wouldn't be too worried. It will idle at a different RPM compared to no AC as having AC on puts loads on the engine. Mine always idles about 100RPM higher with the AC on, and I think its normal.

svo347 · 07-10-2007, 03:11 PM

Quote:

Originally Posted by JC

I6s use a MAP - Manifold Absolute Pressure - sensor which combines air flow and temp into one reading (pressure - being a factor of Volume and Temperature).

Not entirely so, it uses variables sent from the engine temp sensor.. Both the v8 and I6 have two, one for the temp guage and one for the actual eec