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

Hell I can replicate the problem at will! Just open the throttle up to 2000 rpms and hold it for a couple of seconds and it will just stay there even if I push the throttle all the way closed. I'll give that a try (bridging the connector) tonight.

Are you sure the idle switch is working all the time? Using a multimeter, make sure the contacts close when the button is pushed, and if necessary, do a continuity test for the idle switch at the wiring harness at the DME. Perhaps the rubber button on the microswitch is hardened causing it to hang? Make sure there is enough slack in the throttle linkage so the switch closes consistently. Also, make sure there is nothing in the way of the throttle linkage that would cause it stick or hang. Adjust the base idle speed per factory procedure at Kevin mentioned, but it sounds 'possibly' it may not be set right. Bridge b and c on the test socket on the left side of the engine compartment, and adjust base idle speed for 84-86 at 800 rpm. 87-89 at 880 rpm.

http://forums.pelicanparts.com/uploa...1080321730.gif

Kurt,
My car has an '86 engine in it. It does exactly the same thing! Linkage isnt hanging up but the idle hangs at 2,000 RPM until I blip the throttle. If you figure it out maybe you can fix mine in September at the car show? He he he...

Kurt - did you ever get to the bottom of this?

I have what sounds like an identical problem with my UK '88 Carrera.

IACV is clean and I've checked the idle switch operation. The car is hanging onto the revs when hot. As with you I do not believe this is a 'mechanical' problem (i.e. to do with the throttle linkage).

ANy further thoughts? I have recently replaced the DME simply to give me the old one as a spare.

My 1987 had the identical problem. I went on a 2000 mile trip this summer and now it very rarely does it. I did run Techron on the trip. I have no idea if any of this is just coincidence but something definitely changed. I just hope it changed for good! I have probably put on 2-3000 miles since that trip and it is running fine.

This happens with my 80 SC as well. I can bring my down by letting the clutch out a little while still on the brakes. otherwise it is high enough to just let the clutch out in first. The car will just start rolling.

That's what I thought. Is there any way to chekc the decel valve?

On mine it turned out to be a combination of things. First, the clutch cable was pushing against the linkage down by the tranny, had to do some adjusting there. I also had a cracked connector where the cruise control cable snap into the bracket by the throttle housing. Tie wrap took care of that.

Hi Kurt

Thanks for your update.

I dont have cruise control and have the G50 gearbox with hydraulic clutch actuation.

I've had the revs actually climb whilst not touching the accelerator - makes me think it's not a mechanical problem (with the linkage).

I guess I'll have to check the linkage out thoroughly for problems.

Blatant bump.

Anybody have any further suggestions?

Thanks.

Check out this web site (www.systemsc.com) on Troubleshoot & Diagnostics
pages possible help in solving your problem.

Thanks Loren - I'll take a look!

Check your CHT and IAT when this happens. You can check them at the harness of the DME, after taking the connector apart, and plugging it back in the DME.

Although, I don't know why they would go to 2000 rpms exactly, I could see 1400 but not really 2000. :(

Good luck.

This is my experience with fast idle problem. After a few minutes warm up, my 1987 Carrera 3.2 idle is normal at 850 rpm. After driving for a few miles the idle rises to 1200 rpm at traffic stops. In a hit or miss effort to fix the problem, I was adjusting the black plastic adjustment fitting at the end of cruise control cable and the plastic cracked. Somewhere on this board, I saw someone repair the adjuster with zip ties. I did the same repair procedure, and now the idle at traffic stops falls from 1200 rpm to 1000/900 rpm range. I am thinking the problem is not electronic and replacing the cruise control cable will solve the problem. Any comments or ideas?

Guess I should have posted an update at the time, but my problem was down to a hanging linkage. Once cleaned and lubricated at the gearbox pivot it was fine.

Thanks UK for your update. I'm almost certain my high idle problem is mechanical. Repairing the broken adjuster on the cruise control cable seems to have helped but has not entirely solved the problem. And now I find I can slow down the idle by pulling on the top of the accelerator pedal and drop about 900+/- revs. I'll check and clean the gearbox pivot point. Perhaps that will do it.

Maybe pointless suggestion from a hack mechanic but-

Check the back of your accel pedal, the ball on the end of the linkage snaps in a socket there.

Pedal is most likely nylon, which can swell and tighten the fit in high humidity.

Wouldn't hurt to inspect , clean and put a touch of lithium grease on the ball befor you pop it back in.

Check the linkage from pedal to engine. There's a lot of links and pivots and springs along the way to deal with.

As far as the cruise control cable? It should be adjusted to be without slack, but that's it. It's got nothing to do with throttle operation, other than being a potential obstruction to the throttle working properly! You can disconnect the cruise control cable entirely to temporarily diagnose of course.

I had simular problem with my 84 3.2 would not idle down from 1500RPM from time to time but the idle switch was being contacted by the linkage. But I caught it idling at 1500RPM just as I pulled into the garage and I left it running at the 1500RPM then I pulled the connector for the Idle Stop switch and jumpered the connector and the idle came right down to 900RPM. So don't trust the switch even if it clicks at idle! I just replaced the switch and problem went away.

It is troublesome that your car creeps up 1000RPMs when you unplug the switch. If I unplug the idle stop switch at idle on my 84 3.2 it creeps up about 500 or so RPM to the 1500RPM area.

Did anyone touch the CO adjustment screw on the Air Meter?

Thanks again UK.

Fast idle seems to be solved by cleaning and lubricating linkage at the accelerator and at the bell crank mounted on the driver side of the G50. Diagnosis was simple when I realized a slight tug at the top of the accelerator pedal reduced the RPM from 1200/1300 range to 900. All the chatter here about idle control valves, vacuum leaks, cruise control cable adjusts, timing etc. gets to be confusing. After 6 months of '87 911 diy maintenance, one principle remains true - always analyze the obvious first.