Help needed troubleshooting hunting idle at startup and at low RPM

[Alex599]

Happy new year Pelicans,

I’m in the throws of diagnosing an idle issue , yeah, I know. I’m thinking ICV but I’d really like to confirm before starting to throw parts at it.

The car, a 1984 3.2 with 91 octane SW chip and cat bypass, starts and sits at 1200 RPM for about one minute then idle starts hunting, the car may stabilize or stall. If the throttle is bliped upon startup the idle will hunt erratically then stabilize within seconds. The car won’t rev past about 2500 RPM when cold. When warmed up, the car will still stall and hunt when stopped at a stop sign for example, on the road the issue is not noticeable.

I’ve read through many threads using the search function and here’s what I have verified and/or eliminated the following:

Confirmed ICV is “buzzing” when ignition is on
Cleaned ICV with carb cleaner, nothing of note was observed, no change in idle
Throttle micro switch “clicks” when activated manually
No change in idle when O2 sensor is disconnected
When oil cap removed, engine stumbles indicating no vacuum leak

I have a friend that is nice enough to send me his working ICV in he coming weeks but I thought I’d take advantage of the brain trust in the mean time. And suggestions would be greatly appreciated.

Alex

[jlex]

You need to adjust the base idle setting. Take the ICV out of the loop by jumpering it first (check for other posts on how to do this). Could be the idle is misadjusted, and the ICV is having problems keeping it at the right idle speed.

[Alex599]

Originally Posted by jlex

You need to adjust the base idle setting. Take the ICV out of the loop by jumpering it first (check for other posts on how to do this). Could be the idle is misadjusted, and the ICV is having problems keeping it at the right idle speed.

Ok, update: thanks for the lead Jlex. I jumpered the ICV as explained on the SW website. When I turned the key, the car wouldn’t start, the starter turned, nothing else. It did the same thing when I disconnected the ICV at the unit.

Now, I decided to adjust the idle with the ICV operational. This is where it gets interesting; I ran out of adjustment after one clockwise turn (nothing changed in engine speed) That said, RPM is at 1100 at startup, went down to 880 after about a minute.

What could create an intermittent idle issue like this?

[proporsche]

It could several problems..I would start with the throttle microswitch..then there is a possibility of an vacuum leak...also do you have a oxygen sensor on your 911?

Ivan


and some reading

3.2 Carrera throttle body stop adjustment

[porschedavid]

I have a 1984 3.2 but has not got o2 sensor,What about co level if too rich can make it hunt

[proporsche]

if you have an A/c you can adjust the CO by using the A/C.
The car-engine should be wormed up then put your A/C on and step a little on gas.If the engine dies it is too rich.Play with it until the engine comes to idle with the a/c on without dying...

little trick i learned through the years;-)

Ivan

[jlex]

I think you may have tried to adjust the idle incorrectly.
You're supposed to jumper the ICV while the car is running to take the ICV out of the input loop for idle. You apparently jumpered it first, then tried to start the car... wrong way.
Try again, this time jump the terminals after the car is running and up to temperature... then go to the idle adjustment screw & carefully bring it to correct RPM's for idle (900 for your car, I believe?). Hopefully, you have a meter for this, if not, you may have to rely on your tach. Then remove jumper and let the ICV take over. See if that helps.

[Alex599]

Originally Posted by jlex

I think you may have tried to adjust the idle incorrectly.
You're supposed to jumper the ICV while the car is running to take the ICV out of the input loop for idle. You apparently jumpered it first, then tried to start the car... wrong way.
Try again, this time jump the terminals after the car is running and up to temperature... then go to the idle adjustment screw & carefully bring it to correct RPM's for idle (900 for your car, I believe?). Hopefully, you have a meter for this, if not, you may have to rely on your tach. Then remove jumper and let the ICV take over. See if that helps.

Right you are Jlex,

looks like this was indeed the issue. I jumpered the ICV while the car was running and it instantly stalled. I turned the idle screw counterclockwise a few turns, started the car and jumpered the ICV, it reduced the idle but didn’t stall. A few adjustments and looks like it fixed the problem! I still noticed a surge or two during 5 minutes of idling but nothing major.

Thanks all, you got to love this forum!

Alex