1985 911 Idle Surge Issue

[PorscheLovr]

I have a 1985 911 3.2 Carrera and after the engine has been running and is fully warm, the engine surges up and down when idling. I tried unhooking the O2 sensor, but it didn’t help. Any thoughts?

[Roswell]

Idle Control Value would be my first guess

https://forums.pelicanparts.com/porsche-911-technical-forum/1096070-icv-replacement.html

[FrankM_]

I cleaned my ICV first (slight improv) but needed to replace my Oxygen sensor (84000 miles) and readjust the idle mixture. Then the hunting went away.
(1985 Carrera)


Sent from my iPhone using Tapatalk

[salayc]

Throttle body microswitch? You can feel when they're bad, the little red button sticks.

[cabmandone]

Welcome to the site. Learn to use the search function. There are multiple threads on engine surging at warm idle. IACV, Intake runner gaskets, base idle mixture, vacuum leaks... all likely causes.

Here's one example on the second page
Surging Idle Problem Resolved

If you put "idle surge" in the search bar at the top right, it'll bring up all sorts of threads on the subject.

[mgro1959]

I had same issue on my 86. Got to the point I could hear a whistle on acceleration. I knew I had a leak somewhere. Another forum member had same issue. I backed out idle adjustment screw(19 turns I believe,for reference) to remove it. Added dielectric grease to o ring, re installed and reset idle speed. All is great now. Thanks Rob.

[911obgyn]

Idle and CO adjustment with no vacuum leaks is the key. Use the process bentley manual outlines with ICV bypassed and centered. I use a wide band O2 sender and guage installed in the O2 bung for CO.