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Discussion Starter · #1 ·
So I been having this cold idling issue with my car where it revs up and down for a couple minutes every moring, sometime it will stall out. So i have found and fixed some vacuum leaks which have improved the issue but not resolved it. But recently there has been fuel cut off when I give full throttle and the turbo hits at about 3000 rpms . . . no fun. I have read that this means there is either a vacuum leak causing more air to go in or the solenoid is faulty. The thing is that the cold idling issue has been going on for months now so it wouldn't make sense if the vacuum leaks (lets just assume the vacuum leaks are the issue) causing the cold idling issue are now suddenly causing the fuel cut off issue. So I think the solenoid valve needs to be replaced but I'm wondering if you have a faulty solenoid could it cause vacuum leaks?:confused:
 

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...recently there has been fuel cut off when I give full throttle and the turbo hits at about 3000 rpms . . . no fun. I have read that this means there is either a vacuum leak causing more air to go in or the solenoid is faulty.
That's not so.
Your cold idle problem is common for that year and is unlikely to be related to whatever boost problem you have.
Describe your symptoms, not what you think the cause is. Do you know that fuel is being cut off? If it just "falls on its face" when boost reaches a certain level, it's often a loose or cracked intake bellows or connector bleeding off boost. These can be hard to find because they only leak under boost.
 

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Are you using hi-octane (premium) fuel? If you're running your turbsey on regular gas you could be getting a knock as the turbo spools up. The APC will then shut'er down until the boost level drops.
 

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Discussion Starter · #5 ·
@jimmesthene the term i would use to describe it is that the car is "bucking"
Basically the revs go from from lets just say I'm at 3500 rpms they would drop very quickly to about 2000ish then shoot back up to the normal 3500rpms and then back ect. ect. until i lay off of the throttle. Every time the revs drop the car luches forward

@dmgb5 I'll write that down and look at it soon. I have been messing with this for quite some time.
 

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Discussion Starter · #6 ·
Are you using hi-octane (premium) fuel? If you're running your turbsey on regular gas you could be getting a knock as the turbo spools up. The APC will then shut'er down until the boost level drops.
Yes I'm using premium . . .this is what I should be doing right?
 

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@jimmesthene the term i would use to describe it is that the car is "bucking"
Basically the revs go from from lets just say I'm at 3500 rpms they would drop very quickly to about 2000ish then shoot back up to the normal 3500rpms and then back ect. ect. until i lay off of the throttle. Every time the revs drop the car luches forward
That does sound like it could be a leaking rubber bellows. Sometimes it's accompanied by a "whooshing" or "hooting" sound.....Sometimes not.
You have to examine the clamped connections and seams carefully. Sometimes you can flex or squeeze them and get a reaction while at idle.
What is your boost gauge doing when it bucks? What happens when you bring the boost up very slowly?
 

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Yes I'm using premium . . .this is what I should be doing right?
Yep. If you're using premium gas follow Jim's troubleshooting. Could be as you're boosting up, it's deforming some hose/tube/bellows somewhere and causing an air or vac leak.
 

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Discussion Starter · #9 ·
@jimmesthene The Turbo gauge goes somewhere in the red but I don't remember quite exactly I'll look tomorrow when I'm driving. Also on a rare occasion it doesn't happen at all and the car will accelerate, I have never driven another c900 turbo so I don't know if the boost that I'm getting is normal but I usually do pulls in 2nd gear when I test this issue . .. .just fyi. Also my car is an automatic.

Also I replaced the turbo compressor boot right where the bypass valve connects in .. if you know what i mean and the bypass valve is new
 

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Discussion Starter · #10 ·
So I today I put in a new turbo solenoid valve (quick shipping;ol;) but it didnt fix the issue. the previous owner (ex-saab mechanic) says to just fiddle with the over-pressure switch and make it so it doesn't shut off the turbo anymore. But this could tear apart my transmission because the car would be producing more power . . .and its an automatic. could it be the wastegate being stuck completely open so the apc cant reduce the turbo pressure and it just cuts the system out completely by cutting the fuel?

oh and the turbo gauge goes a solid half way into the red
 

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Sounds like an overboost, which according to my FSM could be a few things. This is what is says
1. Leak in hose at APC solenoid valve or bad solenoid valve.
2. Leaky wastegate diaphragm unit.
3. Leaking hose to pressure sensor or faulty pressure sensor.
4. Wastegate sticking closed or binding.
5. Incorrectly adjusted charge pressure.
6. Faulty pressure sensor or APC control unit.
 

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sbvaeth;2129962I'm at 3500 rpms they would drop very quickly to about 2000ish then shoot back up to the normal 3500rpms and then back ect. ect. until i lay off of the throttle. Every time the revs drop the car luches forward .[/QUOTE said:
The lurchering forward when the rpm drops, makes me wonder if you don't have a transmission problem and not an engine.. if it is slipping at the higher rpm and pulling at lower rpm... or am I mis understanding what you are trying to say?
 

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When the overboost switch activates, people usually describe it as "hitting their teeth on the steering wheel" rather than "bucking". Overboost is very violent although it may be less so on an automatic.
 

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Discussion Starter · #14 ·
@geoffweeks its not the transmission its the fuel cut off you'r probably just not understanding it correctly . .I'm not the best explainer either

But anyways I just got rear-ended today so I'm really not worrying about this. . . .****ing jeep drivers think 4wd is going to help them stop
 

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@geoffweeks its not the transmission its the fuel cut off you'r probably just not understanding it correctly . .I'm not the best explainer either

But anyways I just got rear-ended today so I'm really not worrying about this. . . .****ing jeep drivers think 4wd is going to help them stop
Well, what confused me was you said it lurched forward when the speed dropped, which would indicate when the speed (rpm) rose, the road speed did not. Why do you think it is the fuel cut-off?
 

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Discussion Starter · #16 ·
it lurches forward in the sense that all the acceleration stops causing the momentum of the car to like move forward . .. idk how to explain it but a mechanic drove it and said the fuel is getting cut of
 
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