Another Surging 3.2 Idle
 

I have reviewed most all of the surging idle threads and have gotten a lot of information. But having a difficult time applying it to my situation. Idle surges at start for 45 seconds or so, then settles in at around 800-900. Drive it away and the surging starts at all idle conditions. Get up to operating temp, still surges. Take the oil filler cap off and it surges for a moment, tries to settle into a steady idle, but then starts an erratic surging. At least the “normal” surging it regular

Have a new O2 sensor
Have a new head temp sensor
Have a new aftermarket ICV (bought from Germany)

Thinking this sounds like a vacuum leak but I am not savvy enough to know. Could I get some opinions?

Turn the idle screw on the throttle body clockwise in small increments.

You need to set base Idle and CO.
There is a procedure in Bentley manual how to jumper ICV when warmed up and adjust idle speed.
You may get away with that. Otherwise you will have to set CO with a CO meter before the cat, a wide band O2 sensor plugged in to O2 sensor bung, and fiddling with idle screw and CO mixture on airbox.
First thing to check is Idle switch at throttle body.

Idle adjust screw as Dave noted. When was the o-ring last checked? How many turns out from closed is it?

After 40 years that o-ring may be a bit hard or even cracked, letting unmetered air past, causing the ICV to fluctuate more than necessary and result in idle surging.

Which o ring?

Before diving in there, check the idle switch adjustment.

Thanks to all for the advice. I will see what progress I can make

https://forums.pelicanparts.com/porsche-911-technical-forum/351514-3-2-idle-adjust.html

See picture first post. Yellow cap covers adjuster screw.

Count how many turns in (right) to bottom out (close) the port. Then remove to inspect or replace. Install new or reinsert old as necessary. Should be between 2 to 3 turns out from closed for base idle, but you will have to find the ideal.

Sounds like an intake runner gasket leak. Get a torque wrench and tighten all intake runner bolts to 18 foot pounds. They can come loose after years.

I would highly suggest getting a smoke machine and testing for any intake leaks.

This is the one I have but there are plenty of options out there including DIY homemade units.

If you're not comfortable performing this test find someone who is. unless you are certain that you don't have any intake leaks all these other suggestions are just random screw twisting.

Ok, I see, the adjuster screw itself has an o ring.

I'll check mine, good tip!

https://www.pelicanparts.com/More_Info/93011091900.htm

https://cdn1.pelicanparts.com/catalo...919-00-OEM.jpg

Thanks to all for the suggestions. But full disclosure, I’ve gotten distracted and then had to go out of town. So I’ve turned it over to an expert. Will report when I get the car back.

For those who care, which may not be many. It was the idle control screw. Was wound almost all the way out. Turned it in and, bob’s your uncle, it is fixed. Checked to be sure the o ring is good and it is. Wish I can take credit, but Zuffenhaus in Scottsdale figured it out. A $200 lesson

Thanks to all for the input.

Thanks for circling back and letting us know; glad you got it sorted. :)

Really glad you ended this thread with the outcome and the fix.

I meant to chime in but packing and moving got in the way...agree with above - glad it's sorted.


Erik

What could cause the idle screw to move or come out of adjustment?

They don't move; they are moved (adjusted...).

Just thinking this through. Agree with 917 that the screw had to be physically moved. It does not have the cover on it, so who knows what has happened. The real reason I weighed back in is after a lot of thought I am totally surprised at the dramatic running issues this one may-adjusted part created. I did not feel confident enough to screw with it, pun intended, but ended up as a simple fix. Adjust until the idle calms down. Big impact for a small part