High Idle Issue

B

Bullet

Registriert
28. Apr. 2010
Beiträge
20
Danke
1
SAAB
900 II
Baujahr
1996
Turbo
FPT
Hi,

First of all, I would like to say hello to all of you Saab drivers out there :smile: and sorry for the writing in English, but my German isn't that good.
I hope some of you cand give me some advice to how to fix my problem:

About a month or so I decided to clean the throttle body on my 1996 NG900 Turbo Automatic. After the job was done, I noticed that in Park or Neutral the idle went up from 900-1000 rpm to almost 2000 rpm. After this, I thought it was a vacuum problem, so I checked all the vaccum lines, changed the throttle body seal and the IAC valve, but to no positive result.

This is how the engine idles while stationary (when I select Drive the revs drop)

Idle while stationary.3gp - YouTube

This is the idle while driving, and moving the selector from Drive to Neutral. The revs just go up and down.....

Idle while driving.3gp - YouTube

I also noticed that while the car is in Drive and moving at slow speeds, it's like someone is pushing it from behind and if I take my foot of the brake it gathers quite a lot of speed, to almost 40 km/h without accelerating !!!

Here is an example:

Speed gain in "Drive" without accelerating .3gp - YouTube

Any ideas to what might cause this ?

PS Sorry for the poor quality of the videos.
 
Any other indications for a malfunction like CEL?

Are you definitaly sure the IAC valve is working? Is the TB fully closed at idle position?

Only other possibility is imho a vacuum leak. Is there a possibilty to do a pressure loss test of the intake?
 
gghh schrieb:
Any other indications for a malfunction like CEL?

Are you definitaly sure the IAC valve is working? Is the TB fully closed at idle position?

Only other possibility is imho a vacuum leak. Is there a possibilty to do a pressure loss test of the intake?
Zum Vergrößern anklicken....

There is no CEL or any other warning light.
Both the old IAC and the "new" one (bought second-hand from ebay from a trustworthy guy ) when are connected it idles at about the same rpm ~1600-2000. When I disconnect the electirc wire that gets power to them the idle shoots up to about 2500-3000, so I guess they work fine. If there's a more comprehensive way of testing, I'm open for suggestions.
I didn't check if the butterfly valve is shut at idle speed. I'll check this afternoon and report back.
The vacuum lines seem ok, I only changed them last year with silicone ones.

" Is there a possibilty to do a pressure loss test of the intake"
How can I do this kind of test ?

thanks
 
You can try to pressurize the intake system by plugging the hose at the AMM and plugging the hose at the TB with a plug. Then the closed system needs to be pressurized (for example with a tire valve in one of the plugs) and pressure drop is monitored with a manometer.

Easier but dangerous way is to spray flammable liquid like brakecleaner at the connections of the intake while the engine is running. If there is a leak, rpm will go up. This method is extremly dangerous if the brakecleaner comes in to contact with hot parts like the exhaust system.
 
I'm no sure what the AMM stands for....

Vh_1a.jpg


Can you please pin point it on this picture ?
 
Air mass meter, sorry you dont have one as this is a T5 car.

Try to close the intake behind the airfilter.
 
wenn einfacher wäre in die deutsche Sprache ich werde versuchen es für Bullet zu übersetzen.
also die erklärungen hier in Deutsch werde ich versuchen in seine Sprache zu übersetzen und an Bullet per PN weiterleiten.
 
gghh schrieb:
Air mass meter, sorry you dont have one as this is a T5 car.

Try to close the intake behind the airfilter.
Zum Vergrößern anklicken....

Ok, so I'll plug the hose coming from the air filter box, and the one from the Throttle body and put a manometer in the circuit to see if there are any pressure losses ?
 
Yes thats it basically. But first check if the TB is really closed at idle.
 
But please not too much pressure! Something below 1bar is sufficient.

And you can check the valve between 1a and 1b in your picture.

Is the CEL lamp OK? Does it light up for some seconds when you switch the ignition key to on?

CU
Flemming
 
I checked the butterfly valve, it sits exactly horizontally on idle, so its ok.
I also checked the CEL light again (with this method http://www.saabcentral.com/~munki/technical/engine/electrical/cel_codes_trionic.htm), and there are no recorded errors.
The PCV valve was changed about a year and a half ago, but I still checked it: it lets air flow from the engine to the throttle body, but not vicevers, so this is good as well.

One thing I did notice though.....while the engine is at a relative cold temperature, it idles normally, like it should. Once it reaches its normal temperature, the idle rises....
My first thought was the engine coolant sensor, but I got that replaced in February.
 
Beside the problem with the high idle, I noticed a funny hissing sound when the turbo kicks in. I've benn driving this car for three years now and before I cleaned the throttle body, there was no hissing sound, no matter how I drove the car.

What could I have damaged when cleaning the throttle body that would cause this problems?
 
Bullet schrieb:
...Beside the problem with the high idle, I noticed a funny hissing sound when the turbo kicks in...
Zum Vergrößern anklicken....

Hi Bullet!

Check the bypass valve. This valves can make some curious sounds when it is defect and can also be responsible for a vacuum leak.

CU

saabca
 
Is there a specific method to check this valve ? What should I do with it ? :)
 
Bullet schrieb:
Is there a specific method to check this valve ? What should I do with it ? :)
Zum Vergrößern anklicken....

To check the bypass valve simply attach an other vacuum line to the nipple and apply suction to the valve. You can do this easily with your mouth. If the valve holds vacuum then it is good. If the valve does not hold suction is must be replaced.​

CU saabca​
 
Did you carry out the pressure test? If there is a leakage that can also cause whistling noise.
 
I did the test for the bypass valve and it doesn't allow air to be sucked, so I think it must be ok.

@flemming

I didn't have the time to find a workshop that can do such a test. I myself don't have the necessary tools or abilities :)
 
If possible have it checked in a workshop with a Tech2 device. All sensor readings and stored codes.
 
The vacuum lines, IAC and PCV valve are all in good condition and in the correct places and pointing the way they should.
There are no CEL lights on, and never were.
Yesterday, I changed the turbo bypass valve, and the two large diameter rubber hoses coming from the turbo and the ones from the IAC and disconnected the battery for half an hour.

The hissing noise is gone, but the idle issue still remains. With the engine cold it runs like a dream but as soon as it gets warmer the revs shot up to 2000 rpm.

I'll try to find a replacement coolant temp sensor and MAP sensor to see if it makes any difference...
 
Changed the map sensor and the engine temperature sensor. No change in behaviour
icon_sad.gif


I guess I'll have to visit a Saab workshop. The closest one is 140 km away, so I'll have to get a day off from work.
​
 
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