Idles up and down and almost dies

[realgren]

Hi,
I've done some research and I'm thinking the issue might be the idle control valve, but i'd like to run it by you guys before buying the parts.

I practically drive my 911 every day, so it never sits longer than 3 days.

After it sits overnight, my 911 fires right up. However, the idle is really erratic. The tach needle kicks up when the engine fires up. Then it goes down to 800, and back up to 2000, then down to 800, then down to 1800, then to 800, then to 1500, then to 800, and finally it settles at around 900/1000 rpm.

After a few seconds idling calmly at 900 or 1000rpm, I start driving the car. I live in a busy area, so I'll go first, second, maybe third gear, and stop at a stop sign for about 2 miles.

During those times, the car doesn't sputter or anything during acceleration. It accelerates nicely. When i get to the stop signs, i'm usually in second or third. I push in the clutch and brake to the stop sign (no useless downshift to second if in 3rd). When i push down on the clutch, the RPM's go down to 400 RMP or some times even practically to zero RPM on the dial. The battery light even lights up as if the car's about to stall.

It's winter in LA, but the temperature isn't anything lower than 47 in the morning, so this definitely isn't normal. This symptom's also getting worse and worse.

The symptoms do go away once the car warms up. However, they are still kind of around. When i come to a light and the engine is warm, i can see that the needle goes down to around 1100, almost stops there, goes to 800, and then back up to 880 (proper setting for a 3.2l with a Steve Wong chip).

My car: 87 911 with the 3.2l. Steve Wong Chip. The engine has around 103k miles. No other mods to the engine.

[techman1]

Certainly sounds like your idle control valve needs cleaning, or replacing. Do a search for cleaning idle valve, should get a lot of procedure tips.

[stlrj]

You might start with the basics like having the base mixture and idle checked.

[Quicksilver]

Any easy thing to check is the allen nuts for the intake manifold. Very common for them to loosen. 18 ft/lbs if I remember correctly.

[scottb]

Originally Posted by stlrj

You might start with the basics like having the base mixture and idle checked.

I had a similar problem. Threw some parts at it (ICV) but the problem continued. Then I had the mixture adjusted by the good folks at TRE, and it's been rock-solid ever since.

Sometimes the easiest fixes are the best...

HTH

[realgren]

Ok, so I took the ICV off and cleaned out. There was a nice coat of carbon residue inside of it. I shook it around and it sounds like it's moving freely.
While I was there, I checked out the throttle body and it seemed to have a little carbon deposit. I cleaned that as well.
I wiped off the carbon residue from the tubes as well.

I turned the car on, and the idle seems back to normal. I'll drive it for a few days and see if the issue comes back. Otherwise, this was a pretty easy fix.

If the problem comes back, I'll have the mixture adjusted. I think it is running a little rich anyway.