Idle Air Control Valve Help?

sigorico · 04-27-2009, 07:59 AM

Hello All. Need a little guidance. I purchased a 1986 911 Carrera and have been bringing it back up to par. It had been sitting for quite a while and needed some TLC. Well I have it moving and stopping but can not figure out a problem with the idle.

It will not stay running. I have replaced the DME relay and the computer. This weekend I cleaned the Idle Air Control valve. I discovered that if I remove the air line to the Idle Air Control valve from the air intake, it idles correctly. If I reattach it while running it dies. Should I just replace the valve or could it be something else?

Thanks,
Scott

T77911S · 04-27-2009, 08:43 AM

i dont know much about your car, but, if you are removing the ICV and opening the line up to let unmetered air in, it is running too rich under normal configuration. have you checked the O2 sensor? do you have a way to check the mixture?

i assume since you cleaned the ICV you checked it and it is working properly.

sigorico · 04-27-2009, 09:01 AM

I don't have a way to check the mixture. I will check the O2 sensor.

Thanks,
Scott

Wavey · 04-27-2009, 09:12 AM

Great thread for setting your mixture with a multimeter:

idle bounce

DRACO A5OG · DRACO A5OG's Garage

DO you have a Bentley Guide? If not I recommend it. Check the OHMs on the ICV. around 20 OHMs Center and one Outer terminal and the two outer should read aroudn 40 Ohms.

While idleing tap on it with a screw driver to see if it helps clear it up.

r-mm · 02-16-2014, 09:17 AM

I rebuilt my 3.2 @ 106k (not long ago) but didn't touch the IAC as the car idled like a dream. After the rebuild everything felt the same except the idle is now slow to come down from about 1900 and sometimes settles around 1250 instead of ~880. Behaves the same if the car is hot/cold. Tapping the IAC a few times, decently hard, with the back of a screwdriver does tend to settle the idle back down below 900 where the lord intended it to be.

Can someone tell me what exactly I should "clean" to bring my idle back on point? Open and hose down with carb cleaner? Couldn't exactly find a thread on this.

Thanks

DRACO A5OG · DRACO A5OG's Garage

Buddies 86 had same issue, we found a vacuum hose disconnected, solved the issue.

I would also remove the IACV and clean it for extra measure, the engine was sitting while waiting for the rebuild so that could cause it to gum up. But again check all hoses.

They did replace the Fuel Pressure Regulator while they were in there, right?

r-mm · 02-16-2014, 10:00 AM

They = me and no I did not replace the regulator - don't often see that one mentioned as a while you're in there item.

r-mm · 02-16-2014, 11:44 AM

Yanked the IAC valve. This thing is basically a big stepper motor with a little throttle at the end, right? So the only thing to clean is the rotation of the little flapper that controls airflow?

After cleaning, I started the car. Idle bounced up and down until I reved it up some after which it settled to a very nice ~900rpm idle. Let it warm up, turned it off and got the same. Thinking I'll just drive it for a while and see if the bouncing gets worse or better.

Wavey · 02-17-2014, 03:42 AM

I cleaned mine several times with the same results as yours - not 100% reliable results. Some times you just have to replace it.

Flojo · Flojo's Garage

Quote:

Originally Posted by r-mm

I... the idle is now slow to come down from about 1900 and sometimes settles around 1250 instead of ~880.

"funny", I have the same phenomena with my SC.
so before, it was oily and intake rubber was worn and gumped, but idled like a charme.

now everything is clean, resealed and torqued, new fuel valves, -lines, cleaned WUR and extra air valve, and and and.

just before it was finetuned thereafter by my porsche pro it ran 2200rpm to settle to 1300.
now it runs 2000 down to 1000.

tuning the throttle (reducing airflow) made it come down to inbetween 1000-900

I'm not worried, but not happy either...

r-mm · 02-17-2014, 04:08 AM

Exactly! I spent a lot of time de-oiling my intake tract during my top end rebuild... Now im wondering what that oil was doing for me. Maybe sealing up some tiny cracks somewhere or dampening out something to do with the iac. Does one lube the iac in any way?

kidrock · 02-17-2014, 06:52 AM

you can lube the ICV with a light dose of silicone spray. I wouldn't use WD-40 unless I was in a pinch because it seems to attract dirt and eventually gum up.

Aside from the possible vacuum leak, I would take a look at my O2 sensor if you haven't yet checked or replace it. After the car is warm, disconnect the sensor at the connector in the engine bay. If the idle clears up, you've found your problem.

P.S.----Wavey's got a good point, also.