need help with idle proble <did many many searches with no result

ertech · 07-14-2009, 01:51 PM

Hi got a idle problem have been using the search function with no result for my problem.
my 89 930 runs great the only problem I have is with the idle .
when cold it idles as it should at 1300-1400rpm . once warm it goes down to 1050rpm
if it idles for a while or after driving the car for a while at 60 MPH once stopped the idle will go to around 1500rpm .
the only way it will go down is if i put it in gear and press the gas to advance a little.I tried pinching the hose from the intercooler to the AAV and the 2 vacuums to the distributor and it still will not go down .
let me know what you all think
Thanks
Erick

mark houghton · 07-14-2009, 01:55 PM

Quote:

Originally Posted by ertech

Hi got a idle problem have been using the search function with no result for my problem.
my 89 930 runs great the only problem I have is with the idle .
when cold it idles as it should at 1300-1400rpm . once warm it goes down to 1050rpm
if it idles for a while or after driving the car for a while at 60 MPH once stopped the idle will go to around 1500rpm .
the only way it will go down is if i put it in gear and press the gas to advance a little.I tried pinching the hose from the intercooler to the AAV and the 2 vacuums to the distributor and it still will not go down .
let me know what you all think
Thanks
Erick

Throttle linkage most likely slightly bent, rubbing somewhere would be my guess. If you stomp quickly on and off the pedal, will it drop back down to normal?

jwasbury · 07-14-2009, 01:59 PM

I was going to say throttle linkage like Mark, or sticking mechanical advance in the distributor. But then I reread your post and you say that it will get up to 1500rpm just sitting idle for a time?

ertech · 07-14-2009, 02:38 PM

just sitting at idle.can It still be one of the 2 ?

ertech · 07-14-2009, 02:39 PM

if I stomp it I will go back down but after a few seconds not imediatly

mark houghton · 07-14-2009, 05:48 PM

Quote:

Originally Posted by ertech

if I stomp it I will go back down but after a few seconds not imediatly

If it goes back down after stomping it, even though a couple seconds later, then it still sounds like a sticky linkage...but why it sticks only after fully warmed up is a mystery.
With the engine off (cold as well as hot), fully depress the pedal and slowwwly release it. Then...and this is the hard part....you need to get your fingers down to the linkage near the throttle body to see if it's fully retracted. You might also be able to crawl under the car (after raising it up of course) and grap hold of the linkage rod that runs up behind the engine to the throttle body.
If everything feels like it's running freely and not hanging up, then you must be having some sort of intake air leak that is leaning things out (expanding when warm and leaking when otherwise it would seal when cold). Rather strange, but check the linkage first.

JFairman · 07-14-2009, 07:42 PM

..maybe your deceleration valve has developed a sense of humor in it's old age

LOWFAT · 07-15-2009, 02:37 PM

I was going to say decel valve

ertech · 07-15-2009, 03:52 PM

update on the car . set the co at 3 ,when the car sits for like 2-3 min it will accelerate on it's own till 1500 . how do I test that valve?
thanks

A930Rocket · 07-15-2009, 04:34 PM

I'm a little confused on the decel valve myself. What I thought was the decel valve, turned out to be the AAV I removed a long time ago.

So where is the decel valve?

mark houghton · 07-15-2009, 04:59 PM

Quote:

Originally Posted by A930Rocket

I'm a little confused on the decel valve myself. What I thought was the decel valve, turned out to be the AAV I removed a long time ago.

So where is the decel valve?

It's the gold colored flying saucer thing dead center and beneath the intercooler. It should pass additional air to the intake post-throttle body when it's vacuum hose is fed full vacuum...as in closed throttle situations.

I don't know enough about them, but would think they have a diaphram inside that allows it to open under vacuum. One would think that failure (like a ruptured diaphram) might allow air to flow when it shouldn't. Small pin hold in the diaphram = gradual climb in rpms as more and more air is introduced. Just a guess....Mr. Fairman may have the right diagnosis here.

9dreizig · 07-15-2009, 05:07 PM

You need to get someone to help you,, disconnect the linkage at various parts and figure out where it's sticking. start with the transmission pivot point, then move to the engine point.
In my case a bit of gease was all that was needed..

ertech · 07-15-2009, 05:17 PM

will try the linkage tomorow . can I acces the pivots from under the car?
is there a way to test the valve?by pinching the vacuum to it can I tell if it working?
Thanks
Erick

A930Rocket · 07-15-2009, 06:47 PM

Is this it? The workshop manual calls it the AAV.

Quote:

Originally Posted by mark houghton

It's the gold colored flying saucer thing dead center and beneath the intercooler. It should pass additional air to the intake post-throttle body when it's vacuum hose is fed full vacuum...as in closed throttle situations.

I don't know enough about them, but would think they have a diaphram inside that allows it to open under vacuum. One would think that failure (like a ruptured diaphram) might allow air to flow when it shouldn't. Small pin hold in the diaphram = gradual climb in rpms as more and more air is introduced. Just a guess....Mr. Fairman may have the right diagnosis here.

A930Rocket · 07-15-2009, 06:49 PM

mark houghton · 07-15-2009, 07:08 PM

Yep, that would be the dude. Technically it's a valve...either open or closed...whereas what most of us (myself include) call the AAV (for high idle when cold) is actually a regulator (since it infinitely controls - or regulates) the amount of air introduced based on engine and internal heating element temperature.

I swear the manual interchanges the AAV and Decel valve descriptions.

Ronnie's.930 · 07-15-2009, 07:23 PM

Yep, that's it . . . the Porsche PET refers to it as the "Vacuum limiter" and it costs over $500 for a new one !!!

My 930 recently began idling very high (1700 or so) and popping quite a bit more off throttle and adjusting the air/idle screw had no effect. I tested the cold start unit and it worked perfectly . . . other previous posts suggested a bad AAV would have these symptoms . . . I have removed it (had to remove the diverter housing to do so - no space to get to it otherwise) and have capped all the associated ports . . . I will put it all back together and test it in a couple of days . . . BTW the AAV was full of black, rusty, murky water (not just a little, but full) . . . it must have been put in a parts washer last summer when it, and many other parts, were at a shop for servicing/powdercoating etc.

Several members of this board have removed this unit and say that throttle responce is much improved (at the expense of more off-throttle popping) . . . I'm interested to put this to the test. There are several old threads about running without the AAV in place . . .

R

WERK I · WERK I's Garage

Quote:

Originally Posted by ertech

if I stomp it I will go back down but after a few seconds not imediatly

ertech,
There might be an even a easier solution. One of the return springs on the throttle linkage has a habit of rusting and breaking. Check your throttle linkage pedestal on top of the intake manifold. Check to see if there's tension on that spring or is if it just sliding around.

jwasbury · 06:13 AM

Quote:

Originally Posted by mark houghton

I swear the manual interchanges the AAV and Decel valve descriptions.

I think we may be interchanging as well. On my '79, there are three separate devices all of which bypass air around the throttle plate. They are: Auxilary Air Regulator (AAR), Auxilary Air Valve (AAV), and the Decel Valve (or Vacuum Limiter). I'm not sure if all of these devices continued to be used in the later years.

Rocket, its hard to tell from the pictures you posted, but your manual may possibly be refering to the AAV, not the decel valve. It is a gold saucer shaped gizmo that looks very similar to the decel valve. The decel valve on my '79 is attached to the factory recirculation valve assembly. Since you've got a long-neck intercooler fitted, I'm betting your decel valve was deleted when the factory recirc assembly was tossed in favor of the 965 style parts. The AAV on my car lives deep in the engine compartment beneath the airbox. It shares its plumbing to the intake manifold with the AAR.

mark houghton · 07-16-2009, 07:11 AM

Quote:

Originally Posted by jwasbury

I think we may be interchanging as well. On my '79, there are three separate devices all of which bypass air around the throttle plate. They are: Auxilary Air Regulator (AAR), Auxilary Air Valve (AAV), and the Decel Valve (or Vacuum Limiter). I'm not sure if all of these devices continued to be used in the later years.

Rocket, its hard to tell from the pictures you posted, but your manual may possibly be refering to the AAV, not the decel valve. It is a gold saucer shaped gizmo that looks very similar to the decel valve. The decel valve on my '79 is attached to the factory recirculation valve assembly. Since you've got a long-neck intercooler fitted, I'm betting your decel valve was deleted when the factory recirc assembly was tossed in favor of the 965 style parts. The AAV on my car lives deep in the engine compartment beneath the airbox. It shares its plumbing to the intake manifold with the AAR.

Great description, and yes we have been interchaning the names! My '87 does not have the AAV as you've described it; only the AAR for cold idle control and the decel valve (which bridges the factory recirculation assembly with the intake manifold). What purpose does the AAV have then? Is it perhaps part of the smog air pump injection system (my air pump is deleted).

Now that we've thoroughly hijacked Ertech's original post, hopefully this will give him a few other potential sources of phantom air getting into the intake. That, and/or sticky linkage to cause the high idle symptoms.