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Discussion Starter · #1 ·
I've been suffering from this problem on and off for the last few months and I've decided it's about time i did something about it...

Occasionally when I start up my 9k (MY97, 2.3T Auto) it'll run very rich for the first few minutes (anywhere between 30 seconds and 10 minutes) before the mixture seems to sort itself out. During this time there's a bad smell of unburnt fuel and it runs as rough as a bears rear end, driving in anything higher than 2nd there's no power.

I can never tell when this is going to happen either - it's not dependent on temperature or weather. If it starts fine then it'll run fine, and equally once the mixture seems to have sorted itself it runs fine then too.

As an example it ran rich for the first 4 minutes of my commute this morning. On leaving the office this evening it ran rich for the 3 minutes it took to drive to the local motor factors and, after being left stood there for 30 minutes, it again ran rich for about a minute before returning to it's smooth self.

The CEL light isn't showing up any faults and the plugs, whilst not new, are in good condition. Vacuum hoses were all replaced about 6 months ago and aren't showing any signs of degradation. Coolant temperature sensor was replaced a couple months ago.

Any suggestions?
 

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I would guess that it might be the oygen sensor, possibly the heating circuit that is used to get it up to efficient operating temperature when the car is first started.

This might not show up as an emission problem, because the computer doesn't make spot decisions on mixture, but uses average readings over time.
 

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Your description of the problem is reminiscent of the Classic and well documented AMM problem.. The thing runs rich (seriously Rich)and idle hunts all over the place.. untill warmed up.
As usual Lotsa $$ replacing yet another Bosch Part (the AMM) will fix the problem :)
 

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Discussion Starter · #4 ·
I'm going to replace the oxygen sensor next weekend, managed to get a reasonable price on a Bosch replacement. Idle is rock steady, no hunting at all.
 

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Discussion Starter · #5 ·
Well, I've replaced the lambda sensor and it's now giving me a CEL code for a lambda sensor fault (which it didn't with the old one fitted).

I disconnected the battery for a hour to clear the memory (as it also came up with a air intake sensor fault - not the issue, sensor is tested and okay) and it still comes up with the 6 flashes for the lambda. I've now also got an intermittent misfire at anything above 1500rpm.

The lambda sensor I took off was Bosch part 0258003662 with 4 wires (2 white, 1 grey, 1 black) and stamped as a Saab part also, the replacement I fitted (from www.justlambda.co.uk was Bosch part 0258003503 with just 3 wires (2 white, 1 black).

Can't swap the new one out for the old one to check as I had to cut the plug off to remove it (the wire runs through a support on the front of the cylinder block which refused to come off so I had to cut the cable to one side of it).

I'm pretty stumped at this point. From cold it starts rich and runs that way for about 10 minutes, and there's still no power. If the engine's warm it starts fine and runs okay - but then I get an occasional misfire above 1500rpm. Any other suggestions?

Cheers

Matt
 

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Replacing a 4-wire sensor with a 3-wire sensor is not a good idea. I don't know for sure, but it's possible that you have installed some kind of (cheaper) universal sensor with no heater wire, and/or the ECU cannot resolve the voltage signals from the remaining 3 points.
As a general rule for O2 sensors, stick to the actual Saab part number unless you have specific knowledge and experience of their operation.
 

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Discussion Starter · #7 ·
Well as far as I can see the only difference between the old and new sensors is the old one has an earth lead on it, whereas the new one doesn't. It started fine this morning but the CEL came on after about a minute.
 

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Don't minimize the difference between a 3 and 4-wire sensor. I've known people spend hours trying to rig up devices with voltage signals to fool the ECU after installing a non-standard sensor, with very limited success. I believe the ECU waits for the engine to warm up before actively checking for O2 sensor errors - about a minute, maybe?

If you are going to keep that sensor, you will need assistance from more knowledgeable members than I. Don't wait too long, because rich mixtures will eventually damage the catalyst.
 

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Discussion Starter · #9 ·
I've spoken to the bods I ordered the sensor from and they're sending me a 4 wire replacement free of charge. Should arrive this morning so I'll fit it during my lunch hour.
 

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Discussion Starter · #10 ·
Fitted the four wire sensor during my lunch hour yesterday, disconnecting the battery for 30 minutes cleared the CEL code once the new sensor was fitted. So far (touch wood) all seems okay, no running rich or rough.
 

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That's good news, congratulations on the way you dealt with your supplier.
The catalyst is probably grateful, too.
 

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Discussion Starter · #12 ·
Seems the new lambda hasn't fixed the problem. Was up in Edinburgh at the weekend and first thing saturday morning the car started up as rough as ever, ran that way for 5 minutes until I parked up, 20 minutes later I restarted and it ran fine. I've done 400 miles since then without any issues. Any other ideas or is it about time I parted with more cash and got it diagnosed...
 

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I'm going through the same problems that you are describing - what we are noticing is that it is almost like the car is running on choke constantly. There are two temp sensors on the head - one for the coolant which feeds the gauge and also controls the cooling fan, and the second on the inlet manifold which is fed into the EMS and is apparently used for something or other.

I haven't had a cost for getting it replaced yet, but don't think it'll be to dear.
Good luck and let me know how you get on.

Kenneth
 

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Klarking - the one on the inlet manifold is indeed used to control fuelling and can produce rich running if faulty. It can also go out of tolerance without creating a fault. It is possible to test it if you want to! (You need a multimeter and a thermometer, a bowl of water, some ice and a kettle).
 

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And the values that I would be looking for are? I suspect it could be faulty because it did get very badly handled when the head was off (for that try reading beaten, hit, poked jabbed, and otherwise generally abused to get the b****y thing out from behind the engine when I dropped it while trying to refit)

Kenneth
 

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20-30 K ohms at -30 deg C
7.0-11.4 K ohms at -10 deg C
2.1-2.9 K ohms at 20 deg C
1.0-1.3 K ohms at 40 deg C
0.565-0.670 K ohms at 60 deg C
0.295-0.365 K ohms at 80 deg C
0.24-0.26 K ohms at 90 deg C
0.14-0.16 K ohms at 110 deg C
 

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Discussion Starter · #17 ·
I replaced the coolant temp sensor back in January as it was coming up with a CEL for it. If I remember rightly it was about £4 from Bowett Saab in Leeds. I'll check the other sensor this evening if I get chance.
 

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Blackstealth,

The sensor that we are talking about is in the back of the inlet manifold roughly in the middle. The one that you mentioned is on the right hand side of the engine (looking from the front). They do different things and the one that I mentioned could cause rough running, where as the coolant temp sensor if faulty may not switch the fan on and as a result cause the cylinder head to warp.

Hope this explanation helps you understand the difference.

Kenneth
 

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Discussion Starter · #19 ·
If we're talking about this sensor here (photo speaks a thousand words and all that)



Then that's the one I replaced at the beginning of the year after getting a 4 flash CEL that wouldn't clear until I replaced that sensor. So where's the other sensor lurking then?

Cheers

Matt
 

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Blackstealth,

A picture does speak a thousand words and that is the little blighter to which I referred. I've just ordered a second one after the first was dropped down the back of the engine with no hope of getting the bleeding thing out. Thankfully they are only about £7 from our local Saab dealer.

In our case, it does seem to be the problem (from further testing) but I'll know more once our Saab dealer gets the part in stock.

Other than that, I don't know.

The obvious two are timing issues and vacuum leak. Both can cause rough running, but the timing is, unfortunately a specialist area.

Kenneth
 
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