Getting strange misfire error codes (???)

[chris_de_ze]

My car is a  MY03 9-3ss 2.0T with 108K Km (67.5K miles) on the clock.
Once in a while I am getting (strange) misfire error codes.

The symptoms started 5 months ago and they happened 3 times so far under always the same conditions: engine cold, first 5-10 minutes of engine operation.

The engine starts and idles OK but when the gas pedal is depressed the engine stalls and a rhythmic noise is heard from the engine. If I depress the clutch  the rhythmic noise goes away but the engine continues to stall as rpm increase. I think the noise comes from the DMF as engine is misfiring and not working properly. At the same time misfire error codes appear. After driving for 5-10 min with engine stalling the car returns completely to normal and no misfires or rhythmic noise any more! Like it never happened before!

(1) On 12-jun-2011 I got:
P0303 : Cylinder 3 Misfire

(2) On 1-oct-2011 I got:
P0301 : Cylinder 1 Misfire
P1312 : Ionization signals implausible, sooted spark plugs
P0137 : O2 Circuit. Low voltage. Sensor 2. [O2 Circuit Low Voltage (Bank 1, Sensor 2)]

(3) On 19-nov-2011 I got:
P0301 : Cylinder 1 Misfire

When the symptoms appeared for the 2nd time I changed the plugs and gapped them to 0.9mm, I cleaned the ionizer module, I switched coil No1 with coil No2 and I changed gas station in case the fuel is the culprit. But the same symptoms happened again after then.  I have taken the car to the dealer twice and I left it there for 2 days each time but they could not find anything wrong since the symptoms never appeared again while the car was there. They could only read the misfire error codes from the ECU but they could not identify the cause since there were no symptoms at all! So no help from there.

Any plausible explanation of what the problem might be?
Is it  a crankshaft position sensor fault?
I am really puzzled and any valuable input is welcome.
Thanks

[littlebasher]

Almost certainly the coil pack i would say...

[chris_de_ze]

I would certainly say the same but after the 2nd time (where I got "P0301 : Cylinder 1 Misfire")
I switched coil No1 with coil No2.
And then the 3rd time I also got "P0301 : Cylinder 1 Misfire".
If it were the coil then I should have got "P0302 : Cylinder 2 Misfire". But I didn't.

Spark plugs are brand new. So that leaves the fuel injector, the ionizer module and the crankshaft position sensor.

[littlebasher]

It's funny, but i was watching a TV program last night where they repair cars and sell them on (Called Wheeler Dealers)

Same car, year and engine as yours and was having a similar fault, coil pack cured it!

But as you say, if you've swapped them around and get the same fault it kinda rules that out

BTW, did you clear the old codes out first before you swapped them around?

[chris_de_ze]

Yes I did. I cleared the error codes after swapping the coils around.

Now I am thinking of swapping No1 and No4 and wait for the next error code occurrence.
And see what happens.

It's OK for me to replace a coil but I haven't figured out yet which one to replace.
All 4 of them will end up to be very expensive (because coils are not cheap).

[Audax]

It almost sounds as if it is a DMF fault where somehow it's getting stuck and the imbalance of the flywheel is putting the engine out, it's a possibility but I can't see think of a reason it doesn't do it all the time. I've seen a few with similar problems caused by the DMF but it's apparent all the time.

[chris_de_ze]

Your reasoning is right. The problem might be the DMF but the rhythmic noise is not always apparent. It happens only every 30-40 days and always when engine is cold and first started. For the first 5-10 min I hear the noise and I see the error code on my scanner. After then the car returns back to normal like there was no problem before! That's what's surprises me. And the mechanic at Saab couldn't find anything wrong with the car twice, except for the error code registered in ECU. From the time I start the car till the time I arrive to the dealer (10 min drive), the symptoms have completely disappeared!!!

Do you the crankshaft position sensor might be the culprit?

[Audax]

If you get this problem and immediately turn the car off and then on again does it carry on doing it? I'm really at a loss to what it could be, it could be the CPS but it could be so many other things too!

[chris_de_ze]

The time I get the strange symptoms I switch off and on the engine many times but  the symptoms remain. I have to drive for 5-10 min and get the engine warmed up enough for the problem to disappear. And then the car performs great! I have also disconnected and reconnected the negative battery post but no cure.

The engine starts fine and idles fine except for the rhythmic noise heard (probably) from the DMF.
When I try to raise rpm (by stepping on the gas pedal) the engine does not respond well and the car feels very underpowered. At the same time an error code appears.

This very strange engine behavior is really doing my head in!
And the most annoying part is that I cannot reproduce the problem at will so I can identify the cause.

[Guyver1]

You say the plugs are new

Did the problem start after the new plugs were fitted?

[chris_de_ze]

No, the problem started with the old pugs in.
When the problem reappeared for the 2nd time then I changed the plugs with new ones.
But the problem came back again after a month or so.

The major difficulty here is that the problem is not permanently apparent. It comes once in a while every 1-2 months, it lasts for 5-10 min and then disappears by itself after 5-10 min of engine operation. This is why it's very difficult to diagnose the cause. However, the conditions under when it happens are always the same: engine cold and when first started. Otherwise the engine performs great.

[Max Headroom]

To me, that sounds like a blockage, or partial blockage of something.

[Audax]

Reading this again makes me think this is possibly a fault with the SAI system, has your car got the upgraded MY03 software for T8? The early cars had numerous gremlins and the updated software fixed many of them.

[chris_de_ze]

The SAI system works fine and only for the first 20-30 secs from a cold start. After then it's put out of operation.
Few months ago I had the SAI valve replaced (at 60K miles). Not because it was faulty but as a precaution measure to avoid subsequent SAI pump failure in case the valve fails.

[chris_de_ze]

I thought I'd come back to this and post some update just for reference to other forum members.
Seven months ago I replaced all 4 ignition coils (Mitsubishi part # H6T60271, Saab part # 12787707).
Since then no error codes or misfires!
Probably that was causing the problem.