Strange Engine Starting Issue

[glenmore3685]

Hello

I've got a strange issue with my car (2007 2.0T Saab 9-3 Aero auto estate).

The car starts fine from cold and runs with no issue. If I drive the car and get it up to temperature, then park it and switch off and come back to it about 5/10 minutes later it starts and dies immediately:

Video

If I use the accelerator then it will stay running, run rough for a few seconds and then be completely fine (as I did on the 3rd starting attempt on the video).

I took the car to my local specialist and they were a bit stumped. We mistakenly thought the issue only occurred when the car is full of petrol and they replaced the evac purge valve as there were no codes on the ECU and they were pretty stumped at what else it could be and this is a common problem for the 2.8T engine. This did not resolve the issue however.

I then tried a couple of straight forward fixes myself and cleaned the MAF and MAP sensors and then throttle body, again these have made no difference.

I'd love to get to the bottom of this issue but want to try and avoid the 'replacing parts until I find the right cause' scenario!

As the car will start if you give it some gas makes me think its not an immobilizer/ignition fault, it feels like it could be fuel starvation, although I'm clearly no expert.

Any help would be most appreciated.

[glenmore3685]

No idle control valve on my engine, there is a tiny gap around the butterfly to control idle.

Throttle body is probably at the top of my list on what to replace first, although your suggestion of the basic items first is probably a good shout. Just feel if it was plugs or filters the issue would be more consistent and appear more often than warm starting?

[glenmore3685]

Will do, not sure how I can test the fuel pressure - hopefully someone in the know comes along soon :-)

I've had the car 10 months and I'm pretty please with it aside from this issue. I could live with it but the idea is for my wife to be the main user so I want to get it sorted as I don't think she'll appreciate a car with an intermittent starting problem!

CPS is another common failure point on these cars but I don't get any error codes and my garage said if that was on the blink the rev counter doesn't move when you try and start it either.

[glenmore3685]

Thanks for checking.

Do you think fuel is the most likely suspect? As you can see from the video it does appear to start, albeit for a split second and then it completely dies. Would this be synonymous with too much fuel (flooding) or too little? If there was a fuel starvation issue would it not cough and splutter and then stall?

I have ruled out ignition initially as a dab of the accelerator sorts its out, but I'm no expert so happy to be corrected.

[glenmore3685]

Cool, thanks both. Will try and replicate it and go and listen out for the fuel pump. Then I'll start to narrow it down by replacing the basics if it doesn't lead to anything.

[glenmore3685]

Peanut Gallery said:

This. I had loads of this sort of problem with my manual fuel pump carb cars. (as opposed to electric fuel pump) - drove me mental on hot days.

Somewhere fuel is vaporising, and there is just enough fuel left to get the car to fire. What happens if you turn the ignition on, wait for 5 seconds or so for the fuel pressure system to bring itself up to full pressure, then try start?

Just to clarify it is an electric setup in my car. I will give it a few seconds next time and see, but I'm sure I've given it an adequate gap in previous attempts but it didn't seem to make a difference but I'm not 100% sure.

[glenmore3685]

Also just to clarify if I try and start the car immediately after I've switched it off, its fine. The problem only manifests if the car is left for 5 minutes or more, or once the engine is completely cold its fine.

Edited by glenmore3685 on Monday 9th November 11:31

[glenmore3685]

bearman68 said:

If you have no particularly sophisticated tools,it's worth just lifting the back seats and listening for the fuel pump when it doesn't start.


Cheers

OK so I tried to replicate it today and switched the radio off so I could listen out for the fuel pump. Replicated the issue and I could hear the fuel pump working quite hard when I tried to restart it. Not sure what that proves now though!

[glenmore3685]

Correct, there were no fault codes when I took it into the garage. I also haven't got a CEL since either.

Taking the injector rail off is probably a bit beyond my basic abilities, I guess the alternative would be to check a spark plug afterwards to see if its wet?

[glenmore3685]

Pumaracing said:

Starting ok from cold but not hot can be due to overly rich mixture and failed coolant temperature sensor.

Starting from hot is fine, its starting from a hot engine that cooled down for 10 minutes or more where the problem occurs. Once its completely cold again its fine.

[glenmore3685]

That makes sense, thanks for the explanation.

Will check the temp sensor, are there any obvious ways of testing if its faulty or is it just a case of swapping it for another one and seeing if that cures it?

Would cutting out due to a rich mixture normally generate a fault code on the ECU?

Edited by glenmore3685 on Tuesday 10th November 14:43

[glenmore3685]

sploosh said:

Clocked over 200k in my Saab. They're great cars, but they do suffer from quite a few common problems.

My money is on the Crankshaft Position Sensor. If it is intermittent fault and you're not getting a warning light on the dash the diagnostics may not be showing the issue. DIY job if you're keen or I HIGHLY recommend Bagnall Saab if you're anywhere near Birmingham.

The other thing to do as a matter of course is to replace all the rubber vacuum hose with silicone. Easy DIY job and you'll save pain later on when you get odd faults as the rubber perishes..... possible your fault is down to vacuum leaks but in my experience leaks usually cause stalls when the engine is warming up ..... i.e. the first junction that you stop at in the morning.

Edited by sploosh on Tuesday 10th November 18:11

Thanks for the advice, the garage didn't seem to think it was likely to be the CPS. They said if it was the rev counter wouldn't move when you go to start the car. Also I think a failing CPS would manifest itself in other ways rather than the specific scenario that my issue occurs in.

Edited by glenmore3685 on Tuesday 10th November 19:16

[glenmore3685]

Pumaracing said:

The ecu doesn't know there's a problem if the temp sensor fails. It just thinks the engine is cold.

Yes I understand that, what I meant was wouldn't a stall down to a rich mixture be picked up by the ECU?