Slight misfire at idle? B207.

[Steve McF]

Moving the Aero in and out of the garage (2006 B207 2.0T Aero), -when it idles it sounds like there seems to be a slight misfire from the engine, but it drives fine. Any thoughts on what to look for? No error codes or engine warning lights.

I have another set of coil packs so could try them. On the Saab Facebook groups it's been suggested it could be plugs, coil packs or exhaust valves.

Any thoughts?

[sgould]

The valve problem was mainly from 2007 onwards, and usually gives code.

You need fuel, air and a spark for ignition.  So I would be checking the coils and plugs. And also the injectors.  There was an issue with the wiring cracking in the injectors.  No. 3 cylinder usually goes first. Saab did a wiring repair kit, but it was just wires and connectors.  Has the heat cracked the plastic sheathing on the wires?

[Audax]

And also the injectors.  There was an issue with the wiring cracking in the injectors.  No. 3 cylinder usually goes first. Saab did a wiring repair kit, but it was just wires and connectors.  Has the heat cracked the plastic sheathing on the wires?

That's a 1.9 diesel problem, doesn't affect B207.

[Audax]

I have another set of coil packs so could try them. On the Saab Facebook groups it's been suggested it could be plugs, coil packs or exhaust valves.

You could try them but in reality you might just move the the problem around, I think you said you want to keep the car long term so in your situation I would be more likely to just buy a set of 4 brand new (genuine!) coils and 4 brand new spark plugs (of precisely the same brand and model as specified by Saab), you can get a set of 4 genuine coils from reputable sellers on ebay for £168, the plugs are probably another £30-£40.

[sgould]

And also the injectors.  There was an issue with the wiring cracking in the injectors.  No. 3 cylinder usually goes first. Saab did a wiring repair kit, but it was just wires and connectors.  Has the heat cracked the plastic sheathing on the wires?

That's a 1.9 diesel problem, doesn't affect B207.

Yes, you’re quite right! 

[Steve McF]

Cheers guys, yes no intention of getting rid of the the car - since we moved house, it now spends more time sitting in the garage than out in all weathers on the drive. I tend to use it for a week or two, then swap back into my Peugeot 107 for the next week or two, keeping the mileage down on both

So it sounds like coils or plugs. Does the comment I got about exhaust valves sound like another 'possible'?

I take it it is fairly easy to change coil packs?

[sgould]

Cover off, and the coils are 1 bolt and a connector.  You may need a thin walled plug spanner for the plugs, but I can't remember.  I had to get a thin walled one for the V6.

[umma08]

Cheers guys, yes no intention of getting rid of the the car - since we moved house, it now spends more time sitting in the garage than out in all weathers on the drive. I tend to use it for a week or two, then swap back into my Peugeot 107 for the next week or two, keeping the mileage down on both

So it sounds like coils or plugs. Does the comment I got about exhaust valves sound like another 'possible'?

I take it it is fairly easy to change coil packs?

Is it a 107 Rallye you have?

[Steve McF]

I think it is on the V5 as a 107 Sport, but they are all the same, with the same Aygo engine, so it is no more sporty than any other C1/107/Aygo

[Steve McF]

Well I found that set of spare coil packs I have the other day whilst looking through boxes of bits. I might try swapping the whole set and see of it makes any difference

[sgould]

Coils can fail if they are trying to fire a faulty plug.  So it's best to change the plugs at the same time, just in case.  Otherwise the bad plug could damage a new coil.

[Steve McF]

But wouldn't that cause the car to run rough when driving as well as at idle? Car drives fine, so it seems?

[sgould]

Possibly.  A Tech2 session or a good code reader may find a "pending" code.  This is common on misfire counts which are approaching a warning level, but not there yet.  Tech2 would also find the misfire counts for each cylinder, which may show one cylinder hiher than the others.   A good reader or a smartphone app might find these too.

[Steve McF]

Back to this again - car is due a service, but a couple of months back I did try swapping coil packs with some other ones I had got from a breakers. I thought that by changing one or two, the idle had smoothed out a bit (tend to get some idle vibration in the car, and also still have the fluctuating idle issue which may be related to the a/c compressor, which is working but getting noisy).

However, the other day, manoeuvring the car into the garage and getting out to check how far away I was from the stuff behind, I heard the sort of popping noise coming and going again. The engine speed fluctuates a bit, and as it is doing so, there is a pop noise coming back through the air intake and into the air filter box. Not very loud, but noticeable.

I've had the car almost 5 years now, and no one has ever diagnosed what this is, and it doesn't seem to adversely affect the every day running of the car, or show up on Tech2. So I'm still baffled!!!!!!

Any ideas?

[sgould]

 It sure.  But if it’s a backfire, on an injection engine, it could be a leaky/ sticking inlet valve.