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Discussion Starter #1 (Edited)
for the last few days my girlfriends 96 900se (5spd, 140K) has been stalling every time you put it in neutral. :cry:

heres what i can tell you (that matters):



  • it has, and has had for months a CEL (when last checked was for a bad rear o2 sensor)
  • air filter is clean, recent fuel pump & filter replacement, oil is full, de-carboned inside of intake track/head with seafoam spray.
  • compression is good.
  • plugs look ...ok. hard brownish buildup on backside of electrode arm only, but is clean between points and everywhere else.
  • car has idled/run fairly poorly since i've known her (8 mo.), thought it was the o2 sensor.
  • car has always run fairly low on the temp. gauge.
  • in the last month (about 6 times) the idle has quickly lumped between ~2000rpm and ~800rpm.
  • slight black cloud from exhaust whenever going into boost.
heres what has been happening for the last couple days:

  • start the car, idles by itself ok
  • for the first ~1min (while the ecu is in closed loop?) the car idles up/down about 2-300rpm from normal. if car is turned off momentarily this can be repeated. sounds almost like a misfire?
  • after the first minute (ecu goes to open loop?) the idle smoothes out and is steady at about 1100rpm. runs fine.
  • after a while of idling it will become rough, idle low and really lumpy, almost stall, then jump up in rpms to ~1600rpm, then repeat.
  • once the car has been under way and under load for a bit, everytime you push in the clutch it stalls almost immediatly.
  • car is easy to restart.
  • vac/boost gauge reads vacuum at idle as pretty close to 0. its probably at less then 10in hg, whereas a normal car would be at 20in hg. it is also slighly fluctuating, and this is at any time during open/closed loop operation.
any ideas on what to check?
i'll try to get the codes pulled later today, but it isnt that easy around here.
i'll also try replacing the plugs.
thanks people.
 

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I had similar thing twice. Once when my DI cassette died and second time, when I had false air in the intake. These are the two most common things I guess. If you can, then borrow a DI cassette from some other car and see if that helps. Also check if some of the intake connections didn't come loose.

 

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Sounds a lot like a dirty/sticking idle control valve, this is supposed to catch the falling revs and bring the engine to a controlled idle, if is sticking it is unable to rspond quickly - engine dies; if it responds just in time the engine almost stalls, but the ecu will kick the valve open to bring the revs up and back down slowly, the best way to sort this [if indeed it is this] is to remove the item and give the airways section of it a good soak in petrol overnight, the lube with a very light oil or silicone spray.
 

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Discussion Starter #4
the idle valve sounds like a good bet. where is it located?
on most cars that i've delt with its connected right off the throttle body. i'll check there when my girl gets home with the car later.

my mom has the same car and i can swap the DI cassette between the two of them and see if that solves it as well.

two great suggestions, anyone else?
 

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The brown cloud from the exhaust probably means the air/fuel mix is off, most likely running too rich. The front O2 sensor has a lot to do with how the ecu adjusts the fuel, so I would make sure tehre is not CEL code related to the FRONT O2 sensor. The rear O2 sensor just monitors the state of the catalytic converter, as far as I know, it is not used for engine control.
 

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One more easy thing to do is to check all the vacuum hoses-- it is very likely that a car this age has brittle or broken lines, and this can be a major source of uneven idle. If they haven't been replaced to your knowledge, you should probably do them anyway, as they will eventually leak. There are four 4mm hoses of various lengths, and a larger one to the purge valve (just replaced that one myself, and was relieved to find it cured a surging problem-- was really hoping it wasn't the DI!).

Good luck, and please post back when you figure out what fixes this.

Regards,
T
 

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ragtopcav said:
the best way to sort this [if indeed it is this] is to remove the item and give the airways section of it a good soak in petrol overnight, the lube with a very light oil or silicone spray.
Second this. Instead of soaking in gasoline, though, I sprayed liberally into both ends with carb cleaner (nasty stuff) until the liquid ran clear, then followed with q-tips. Didn't use oil after but probably should have. A lot of folks do the butterfly valve in the throttle body at the same time.

T
 

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Yes, that the idle air control is either sticking or completely malfunctioning, is the most likely cause of this problem AND, its cleanliness IS a service item ( or officially should be)...

Another thing which is wrong is "running too cool".
This is NOT right - after checking the true operating temperature- most likely the thermostat should be changed..
To check the "true operating temperature", I wold love to use one of those HVAC electronic infra red heat detectors for this purpose..
 

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Discussion Starter #9
i tried cleaning the IAC but its the bosch type which doesnt come apart apparently. i'll try soaking it in gas though.
the auto parts place said they cant pull the codes till next week.
i'll try swapping both the DI and the IAC with my moms functioningg ones tomorrow morning and see what that does.
 

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The IAC doesn't come apart. Once you get it out of the car, trickle a solvent (gas or other) into hose holes in both sides to clean out its interior. You can leave the solvent inside there as long as you want, but I wouldn't soak the whole thing. You'll know it's clean enough when the gate inside moves freely (poking with a Q-tip helps you tell this) and isn't black any more. Swapping with a known good one sounds like a good idea, BTW.
 

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Discussion Starter #11
the codes havent been pulled yet but i switched both the IAC and the DI cassette and neither made any difference. any more ideas?
 

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turbo93impreza said:
the codes havent been pulled yet but i switched both the IAC and the DI cassette and neither made any difference. any more ideas?
Vacuum or boost leak work be my guess since the above had no affect.
 
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