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lambda sensor mystery

3697 Views 18 Replies 7 Participants Last post by  Matthew
Hi again, my car has recently deterioted to the extent that performance seems sluggish and jerky, i'm over fuelling big time, using way too much petrol, and the idle is between 1500 and 2100 all the time.
I noticed something rather interesting looking back at the service history, basically within the last 5 thousand miles it's had 3 lambda sensors!!
The advice says Lambda sensor fault occurs persistantly, faulty signal.

What I am wondering is, are my symptoms relative to this and what on earth could be making the sensors go wrong so quickly? What do i do next?

Please help, I'm supposed to be driving across europe in the next 2 weeks, this is a cry for help.
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Perhaps dead lambda sensors are the symptom of chronic over-fuelling, rather than the cause? Measure the NTC sensor's resistance; details in the Bentley manual if you have one?

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I'm pretty sure Matthew's right--the over-rich mixture is poisoning the sensor:eek:

If the NTC sensor test Matthew recommended turns up nothing abnormal, I'd proceed to test the AMM and the fuel pressure regulator.
I agree - something is destroying the sensor. As well as overfueling a slight head gasket leak can kill it as the anifreeze is poison to a lambda sensor. Also a leaking oil seal on a turbo will choke a sensor with deposits. Any failure of other components like the AMM or the NTC sensor will be recorded as a fault code if they drift outside their operating parameters.
Thanks guys, thats interesting. What is the NTC sensor? does it measure the temperature? I'm trying to pull the fault codes using the instructions on saabwrench, but under my rear seat there is a plug on the drivers side that is blanked off with a plastic lid, and on the passenger sde there is a plug with looped wire, yellow/white colour, is it the passenger side?
Again, thanks and sorry for being a pain in the backside, us amateurs huh
NTC sensor is Negative Temperature Coefficient sensor. If it goes faulty it might think it is cold and mess up fuelling (highly technical explanation) ;) .

The code pulling on Swedish Wrench is specific to American cars, who only got the Bosch system. Yours will be Lucas. There is a guide to pulling Lucas codes in the tech help section here .

Welcome to Saab Central :cool:
A faulty NTC sender would show as a fault code - only a faulty Fuel pressure regulator would not show up as a check engine light fault. If you have a non turbo it will have the Bosch EFI - only the Turbo cars had Lucas.
ok, thanks guys, i'm taking the car to a friends house tomorrow evening to check as much as we can, and I'll let you all know the outcome.
Regarding my system mine should be lucas then because i have a light pressure turbo (as I've heard it called).

Nice to meet you guys, and I have a confession, I own a mondeo:lol: , thats not all, I regulary was a visitor to their forum, which is actually damn good and full of tips, they were a good bunch of people and i thought their forum would take a bit of beating, but I am pleasantly surprised on this one.
I knew that some day I would come back to Saabs, I love em, can't explain it! I was heartbroken when my 9000 CD Carlsson expired I was heart broken when she was written off (non fault accident).

After all these years I've finally got another one, and if it's ill, I'll make it better.

So thanks for making me feel welcome. :cheesy:

The NTC sensor can be found in between the inlet manifold runners for cylinders 2 and 3, and is the blue-capped sensor in the centre of each photograph:

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Hi guys!

I have a new NTC sensor in my garage, but it is for bosch system! I have lucas fpt! Can I use the new one on mine?
Doesn't look like it - the EPC lists different sensor part numbers for Lucas and Bosch equipped cars.

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Hello everyone, hmmm ok, sorry about the long post but, I thought I'd tell you every little querky thing incase it rings any alarm bells.

Today I checked the NTC and it was registering 1300-1500 when the water was at just above luke warm temperature which according to the chart is about right, so it doesn't seem to be this, one less thing though.

We tried to pull off the engine fault codes but to no avail, we just couldn't get it to work. (incidently engine light only comes on say 1 out of 10 times that I start the car.

The fuel pressure regulator has plenty of vacuum and appears to be working correctly.

We also checked all the vacuum hoses.

I cleaned my AIC, although when i tested it the conical plug/small shaft with spring extends down when i start the car, it doesn't fluctuate like it said I should see happening, maybe this is ok? or maybe not?

I cleaned the throttlebody as well, including the butterfly thing.

Wasn't able to locate the lambda sensor, but I know this will have expired anyway, but renewing it would not cure the problem, I also learned that the saab garage who last did the mot recorded a persistant lambda sensor faulty signal, and replaced it only to pass emissions on the mot, they also tried a second hand ECU but it had no effect, so the original ECU was re-fitted. persistant o2 sensor fault uncured...nice.

When I start the car, occassionally the idle is about 1100 instead of much higher, I noticed this today.

We checked for possible head gasket failure and absolutely no signs whatsoever, the water/antifreeze was clear, although a little bit of condensation from the exhaust sometimes.

When I was driving it normally it was lumpy as hell, feeling like it was choking on too much fuel, but I was doing about 60mph and i opened her up and she went like a rocket, and other times/most times she doesn't. seems that when she is using the fuel at higher speeds it has no problem when you put yr foot down (not flooding)

I have no idea, and if a Saab dealership can't find out, then I'm stuffed?

I'm supposed to be going round europe in it in a few weeks and can't afford to put it in a saab garage for them to charge me shed loads for saying they don't know what it is.
why isn't there a smiley that has tears

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Just something which I thought might be worth a look if there's extra fuel getting in there somewhere. Could the cold start injector be leaking/sticking or firing when it shouldn't be? Just trying to think of reasons excessive fuel could be getting into the engine.
Ahhh, thanks..I'll have a look later, any idea if it's easy to do, where is the location of this injector?

The idle only started going high after we squirted carb cleaner into the throttle body so this could have sucked muck and blocked something, but I was still left with the original fuel guzzelling and sluggishness problem, I think the high idling was caused by the cleaning of the throttle body.

Again, thanks for all your help on this, it's well appreciated
Sorry to keep asking questions but I would like to know how you short circuit something, in particular the NTC sensor, the other day I tested the plug and all was fine but not the sensor, and i was just reading an interesting post with a similar problem that I think Matthew had.
So, how do I short circuit it to test this area?
I'm also going to clean out the AMM
To short-out the NTC, remove the connector and loop a short length of wire between its two contacts. The short circuit isn't made on the connector itself. We want to change what the ECU sees on the other end of the cable.

Short-circuiting the NTC cable should simulate a hot engine condition.

When cleaning out the AMM, be careful not to damage the fragile platinum filament. I blasted carb cleaner at everything. Make sure the also clean the temperature sensor which IIRC sits slightly upstream of the filament. It's actually the sensor which gets clogged with rubbish, as the filament has its own self-clean cycle.

If the sensor's buried then the air mass measurement will be offset. I think that would cause the car to run rich...?

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Good news, I cleaned the AMM, and the car now runs smooth, doesn't feel like it's choking or holding back anymore, with fuel consumption time will tell.

But.... have still got high idling, around 2000 rpm, but something strange happens now, after 30 seconds or so the revs drop to 1600 and the engine light illuminates.

So, do you think it's time I now replaced the 02 sensor as I reckon it may be this? causing high idle? possibly something else?

Thanks for your help by the way, you don't know how much weight has been lifted off my shoulders this evening, ahhhhh
not lambda sensor

Since I cleaned the AMM all was smooth for a while (might have been psychological)although there was still the high idling and overfuelling, now the high idling is irratic and sometimes the car starts and runs at 900rpm (correct idle) but soon creeps up to 1500-2000 rpm.
I replaced the 02 sensor, but the old one was ok.

But..... I tested the Throttle control sensor, the black round plastic box on the side of the throttle body, the signals are irratic, it must be feeding the ECU some crazy information, I had it apart and it looks like it works like a scalextric controller where you pull the trigger on the controller and the voltage increases the more open it is.

The multimeter was showing really crazy information, all over the place, so I'm getting another throttle control sensor, I think this little baby is the culprit !
The saga continues,
PS, getting a new hood fitted tomorrow :cool:
You can clean the TPS. Degrease the wiper and track, then clean with some Brasso on a cotton wool bud, polish with a clean rag and then lube the track with a graphite stick :) Should be like new then :)

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