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Hi all

firstly, ill give you some details of the car. It is a 2004 Saab 9-5 hot aero auto (the 250 bhp version) and has done just shy of 130k miles.
I have had a lot of work done to it, lots and lots, mainly due to oil leaks, which are all sorted now

but even since i bought the car about a year ago, it has had this wierd problem. When i am sitting in drive, with my foot on the break (at lights or in the drive thru) the car will intermittently cough. I'm not sure if thats the way to describe it, but it feels like a cough, the car will jolt, the turbo gauge jumps up a bit, the rev counter jumps up a bit (not as much as turbo but then its a bigger gauge)

Now, i take my Saab to a Saab specialist who has been going for 40 years so i take it he knows what hes on about, but hes a bit stumped because it doesnt happen all that often. Usually, i wouldnt worry and would get on with it, but the problem i have is i do a lot of miles, and i dont want to get stranded somewhere, even with breakdown service

So, being as he is very reasonable with me, he has tried a few things without charging me, saying he will charge me if it fixes the problem. The first thing we tried was a part right at the front of the engine (i forget the name, something to do with vacuum pipes - i have attached a picture and circled it) this did nothing

today, he has tried swapping the DI cassette, this did nothing

Next we are going to try the fuel pump

but does anyone have any better ideas because i am stumped

the only other symptom the car has is an eggy smell which i know is being caused by the cat which is more than likely on its way out - i havent decided on replacing it yet though because of this other problem, and with the age and mileage of the car i dont want to keep throwing money at it.

In terms of work done, crank shaft sensor was done which fixed the car cutting out, but didnt fix this issue. Vaccum pipes all replaced and are all attached no issues there.

If anyone could help me out or give me a few things to check, i would be more than grateful. Sorry for the essay, thanks for taking the time to read if you got this far
 

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Hi all

firstly, ill give you some details of the car. It is a 2004 Saab 9-5 hot aero auto (the 250 bhp version) and has done just shy of 130k miles.
I have had a lot of work done to it, lots and lots, mainly due to oil leaks, which are all sorted now

but even since i bought the car about a year ago, it has had this wierd problem. When i am sitting in drive, with my foot on the break (at lights or in the drive thru) the car will intermittently cough. I'm not sure if thats the way to describe it, but it feels like a cough, the car will jolt, the turbo gauge jumps up a bit, the rev counter jumps up a bit (not as much as turbo but then its a bigger gauge)

Now, i take my Saab to a Saab specialist who has been going for 40 years so i take it he knows what hes on about, but hes a bit stumped because it doesnt happen all that often. Usually, i wouldnt worry and would get on with it, but the problem i have is i do a lot of miles, and i dont want to get stranded somewhere, even with breakdown service

So, being as he is very reasonable with me, he has tried a few things without charging me, saying he will charge me if it fixes the problem. The first thing we tried was a part right at the front of the engine (i forget the name, something to do with vacuum pipes - i have attached a picture and circled it) this did nothing

today, he has tried swapping the DI cassette, this did nothing

Next we are going to try the fuel pump

but does anyone have any better ideas because i am stumped

the only other symptom the car has is an eggy smell which i know is being caused by the cat which is more than likely on its way out - i havent decided on replacing it yet though because of this other problem, and with the age and mileage of the car i dont want to keep throwing money at it.

In terms of work done, crank shaft sensor was done which fixed the car cutting out, but didnt fix this issue. Vaccum pipes all replaced and are all attached no issues there.

If anyone could help me out or give me a few tighten the serpentine and get a sparkplug fouler for your cat to pass smog,works


things to check, i would be more than grateful. Sorry for the essay, thanks for taking the time to read if you got this far
 

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I would have checked the spark plugs first, how old are they?
Then the plug leads and coil.

It wouldn't hurt to just change the plugs anyway even if they're fairly new, you might have a bad one. I recommend NGK.
 

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Nothing to do with the turbo bypass valve you circled. Sounds like a poor electrical connection. One possibility is the body to engine 42 pin connector under plastic cover behind the engine. This is often overlooked, disconnect and clean. Assume no MIL. If possible use Tech2 to do a snapshot when this occurs, need someone with tech2 experience.
 

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Jesus!...sounds like your guy has gone looking at all the big-dollar stuff too early.
As stated earlier, plug condition, O2 signals, LTFT and STFT are good places to start.
Did he put in a genuine Bosch CPS?
The cheap off-brands can be very sporatic in signalling.
The smell is indicative of an overly rich mixture.
If it happens mostly standing still with your foot on the brake, look for a big vacuum leaks (not small lines) and intermittent electrical connections.
Has the thermostat been changed in this car?
There is a bank of ground connections for the wiring harness in that area on the intake manifold and the housing.
Make sure the ground leads are all connected, clean and tight. IMSMC...they're four.
The automatic Idle compensation on these cars will try to increase the idle speeds with load.
That could be why you are seeing increases in tach signal as it occurs.
A sudden loss and recovery of combustion event...whether through ignition or fuell interruption will trigger that compensation.
How is the fuel pressure and volume?
Look at all of these first.
 

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stuartk1987

As APC 900 suggests, I'd start checking for vacuum leaks. Once you have done that, check them again. It's amazing how many there are around the engine, surprizing that there's enough manifold vacuum left to do anything ! Don't forget the big plastic pipe from the vacuum pump on the end of the head that goes to the brake servo. Also has a spur and N/R valve down into the inlet manifold. I've seem these shrink slightly over the years and pull out.
Any slight air leak can upset the auto tic-over. You get an imbalance between the throttle and fuelling driven by the lambda sensor. Can cause hunting with even a small leak.

Paul @ Kippen.

p.s. Did I say, check all the vacuum hoses again !
 
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