3.2 Fast Idle Frustrating Problem!
 

I have yet to resolve this problem. My idle keeps hanging up at 2000 rpm. Sometimes a blip of the throttle will bring it back down to 850. It is not related to the throttle linkage as it will even do it with the linkage disconnected. Here is what I have ascertained so far: the linkage is working correctly and shutting off completely at the throttle body. The idle switch is working and the idle linkage is engaging the idle switch, I took off the idle valve and cleaned it, tested it and it is also working correctly. Any other suggestions?

kurt,
hey...haven't you asked this question before? don't make me drive up there man...:D

how about a stuck open auxillary air valve? maybe blipping the throttle temporarily unsticks it.
ryan

kurt,
staying on that theme...try disconnecting the aav while the idle is high and see if it drops back down...also just might have a vacuum leak. have any carb cleaner to spray around the intake/airbox, etc.?
ryan

Thanks for the suggestions Ryan, but a 3.2 motronic setup is nothing like CIS. It doesn't have things like an AAV. And you are correct I did ask this question before, with no answers!

ahhh...they stopped using them after the sc in '83 and you have an '86...oops! sigh..guess i better stick to cis troubleshooting!SmileWavy
ryan

Not trying to be a smart ass Kurt, but did you adjust the idle correctly?

You need to disable the ISV and adjust the idle bleed screw on the throttle body.

http://forums.pelicanparts.com/porsche-911-technical-forum/152278-3-2-idle-problem.html

But I see I already mentioned that above............... Know anybody local who also has a 3.2 so you could borrow their ISV to see if yours is malfunctioning? If yours tests out correctly, the signal for the idle circuit is somehow being duped. Did you check the airflow meter to see if the flapper door is moving smoothly/correctly?

Kevin, I actually used your post from my last thread when I checked everything again last night! Did it exactly the way you described. Flapper door is also working correctly.

Seeing as none of the smart people answered this, I'll take a shot. Thinking out loud...
Edit: Sorry KTL (aka "smart people"), I starting writing this before you posted, it just got posted after yours. No disrespect intended.

First a few data points:
- At idle, RPMS for '84-86 cars should be ~800RPM (880RPM for '87-'89 cars) and ignition timing should be around 3 degrees after TDC
- If you pull up on the throttle lever just enough to trip the switch (listen for the click) or disconnect the idle switch plug, idle should increase about 500RPM and ignition timing advance should be around ~12 deg before TDC.

This would be a great time to get that fancy digital timing light with RPM and advance. :D

From the advance, you should be able to tell if the engine is running on the "idle mode" or is off idle mode. (idle=800rpm, 3deg ATDC, off idle=~1300rpm, ~13deg BTDC)

If engine is running in the "idle mode" but the RPMs are too high I think we can assume the idle switch is working and something else is raising the idle - like intake leaks. Vacuum leaks suck. :)

If the engine is idling but running in the "off idle" mode the computer "thinks" the idle switch is open for some reason.

I have to get some work done today so I'll leave it at that for now. Everyone knows about the intake gaskets leaks so here is a link to a couple of other Carrera vacuum leaks.

Hunting down Motronic vacume leaks: What does the thermo-switch do?

-Chris

Good reply Chris although for clarity I *think* the idle setting may have changed ( stock) over the years so you'll find 3 degrees ATDC and also 3 degrees BTDC. A custom chip ( like from Steve wong) may also use one of these numbers ...or yet another. Still, you're correct...it'll be a long way from 13 degrees BTDC, "off-idle" as you say.
---Wil Ferch

Chris, when I disconnect the idle switch plug the idle goes up about 1000 rpms! I will check the timing for the idle as you suggest tonight.

Good point!
-Chris

When it goes up 1000 rpms is it now at the "2000" RPMs you see when the idle is acting up? Hmmmm.
-Chris

No offense taken Chris. Calling me smart is kind of a stretch. I consider myself pretty dumb most of the time.......... I just type well. :p

Yes professor you ascertain something?

A chip? If so, have to love 'em!

Stock chip.

If the motor acts (idles) at the same RPM when it is acting up as it does when you disconnect the idle switch that would make me think the idle switch (or the circuit leading to it) was not functioning.
Like a bad dog, you need to catch this "in the act" and press the throttle lever closed (towards front of the car) with your finger and see if that fixes it. That throttle only has to hang up by a mm to produce the problem you are seeing.
-Chris

The throttle blip thing is what gets me. If the idle goes to the same rpm as when it "hangs up" when you disconect the idle switch, I wonder if either the throttle doesn't always return and trip the switch or whether the switch is failing, and needs the blip occassionaly to reliably close the contacts. Either way, you're likely on to something.

The fact that the blip cures it sometimes leads me to believe its not an air/vaccum leak.

Chris I am actually pushing down like you describe, I hear the click of the idle switch being pushed down, but still the high idle. I did the circuit checks described in the Bentley manual, but am concerned that when I disconnect the idle switch the rpms go up by 1000 and not 500, but not sure what that really means. Thanks for keeping up with this thread. Everything was running fine prior to the rebuild, so I can't help but think I have some connection problem. At times it will drop down to 850 rpms and idle just fine.

Kurt,
I bashed the idle switch once when I had a motor out. I just had to snap it back together and it was fine. Maybe you hit yours? (I'm reaching here. :D)
Next time this happens, pull off the connector and bridge the connector contacts with a thin paper clip or something. If that fixes it, you'll know it's the switch.

-Chris