Nearly a year ago when my Octy went for a service they said the 2ndary air pump was leaking. A google suggested that this part is just an emissions thing and only operates for half a minute on startup. Given the high cost of replacing it I ignored it and put up with the noise on startup.

A couple of months ago the car started misfiring for the first few minutes on startup but an independent found no fault codes and couldn't replicate it. This was in cold weather. When I got the car back it was fine for about three days then the stutter/misfire came back and got worse. A service and plug replacement seems to have fixed it but it can still bog down easily below 2000 rpm when cold.

So the question is: should I replace the leaking secondary air pump? Is it worth trying to fix it with bolts? Is the misfire likely to have been/be anything to do with the pump? Any other suggestions?

Can't see how the SAI could cause a misfire, it's only active for about 45 seconds on cold start. Drilling out the SAI rivets & replacing them with bolts usually sorts the SAI out.

Your misfire is most likely being caused by a failing coil pack. Call your local Skoda dealer as there is a VAG TSB/recall for some coil packs, & will be replaced free of charge if yours are covered.

MAF sensor failure is also extremely common, & doesn't always cause a fault code, the same applies to the coolant temp sensor. Try unplugging the MAF sensor, & if the car runs better then you have a goosed MAF, if there is no difference then the MAF is unlikely to be the cause. If you have the old type black coolant temp sensor fitted replace it with a genuine revised green VAG part as the black type or aftermarket CTS's always fail.

Edited 17 April, 201313 yr by pauldazzle

Nearly a year ago when my Octy went for a service they said the 2ndary air pump was leaking. A google suggested that this part is just an emissions thing and only operates for half a minute on startup. Given the high cost of replacing it I ignored it and put up with the noise on startup.

A couple of months ago the car started misfiring for the first few minutes on startup but an independent found no fault codes and couldn't replicate it. This was in cold weather. When I got the car back it was fine for about three days then the stutter/misfire came back and got worse. A service and plug replacement seems to have fixed it but it can still bog down easily below 2000 rpm when cold.

So the question is: should I replace the leaking secondary air pump? Is it worth trying to fix it with bolts? Is the misfire likely to have been/be anything to do with the pump? Any other suggestions?

As mentioned the SAI is unlikely to cause a misfire unless you only get the issue a first start up. All the SAI does is run a fast idle for approx 45sec to make sure the O2 sensors are pre warmed on start up to protect the CAT.

Then SAI is not used in normal driving as far as I know.

Your cause of misfire is likely to be a suspect coil pack(which there is a recall still active on old coil packs). However if your car is only a bit laggy low down, you may have a suspect temp sensor or MAF.

Have you run diagnostics on the car to see if any error codes come up?

Thanks to both the above. The coil pack(s?) were replaced under recall and there are apparently no fault codes.

The car was looked at by an independent who couldn't find a problem, and when I got it back it ran perfectly for about two days, then started the misfire again.

A few weeks later I took it to a main dealer for its annual service (this was when the plugs were replaced) and it was fine for a week or ten days. A couple of days ago it started misfiring on startup. A bootful of revs seems to sort this out and all is apparently fine after a few minutes, which is what got me thinking of the SAI. The fact that the car seemed better after being looked at even when nothing was done is a complete puzzle to me.

I'll try the sensors.

When you say cold. How cold ?

Mine and many others used to run a bit pooh with in the first 2 mins. That could be called normal some do don't.

Mine did but doesnt anymore I couldn't honestly say what fixed it. It appeared to fix itself !!!

If its still playing up after a few mins of driving then there could be something wronh elsewhere.

I've noticed on a cold start in the morning that mine will sit at 1200rpm idling for about a minute and if I set off whilst at that rpm there is a hesitation; almost misfire for the first 10 secs when accelerating. So now I just let it idle until the revs die down to the norm and start my journey with no problems.

Sent from my iPhone using Tapatalk

I've noticed on a cold start in the morning that mine will sit at 1200rpm idling for about a minute and if I set off whilst at that rpm there is a hesitation; almost misfire for the first 10 secs when accelerating. So now I just let it idle until the revs die down to the norm and start my journey with no problems.

Sent from my iPhone using Tapatalk

That exactly how mine used to go and how I got around it !!!

Like I say it stopped a few years back, don't know why !!

Mine does that too. it's really twitchy at cold start up. It's as if it it trying to boost even on a quarter throttle. It's fine 1 minute after starting though.

I did hear its a normal thing to happen which is why it doesn't worry me. Apparently on a cold start the secondary air pump does this to ensure certain parts reach temperature correctly before setting off (my technical skills of what and why on this subject are virtually zero!) and basically this is the function of the pump...... Really hope someone can shed some light on this though!

Sent from my iPhone using Tapatalk

As mentioned the SAI is unlikely to cause a misfire unless you only get the issue a first start up. All the SAI does is run a fast idle for approx 45sec to make sure the O2 sensors are pre warmed on start up to protect the CAT.

Then SAI is not used in normal driving as far as I know.

Your cause of misfire is likely to be a suspect coil pack(which there is a recall still active on old coil packs). However if your car is only a bit laggy low down, you may have a suspect temp sensor or MAF.

Have you run diagnostics on the car to see if any error codes come up?

Ok..... So I really need to start reading things first! Lol

Sent from my iPhone using Tapatalk

Ok..... So I really need to start reading things first! Lol

Sent from my iPhone using Tapatalk

lol no worries.

The issues most folks mentioned on this thread are the timing between the SAI running it's normal course of pre warming the cat, which causes the fast idle rpm and the cut off of the SAI. That slight few seconds of cut off can cause a hesitancy As David 8 states some cars suffer this and some don't and it is considered a normal running issue.

sometime's a leaking SAI can cause this , or a faulty temp sensor that can't deal with the temp change form the fast idle running. Or a combination of both.

My fix was a change of temp sensor and let car warm for approx 45 seconds and no issues.

Then my permanent fix was junk the SAI and delete N249 and N112 valves and other breather simplification stuff. Less to go wrong then.

I guess mine is normal then- doesnt ever drop and dip the revs like its going to cut off. Just the fast idle for a min and then back down to normal. I just let it do its thing in the morning before driving it lol.

And are there not drawbacks to removing any of those bits?

Sent from my iPhone using Tapatalk

I guess mine is normal then- doesnt ever drop and dip the revs like its going to cut off. Just the fast idle for a min and then back down to normal. I just let it do its thing in the morning before driving it lol.

And are there not drawbacks to removing any of those bits?

Sent from my iPhone using Tapatalk

Yours indeed sounds normal.

No drawbacks at all. They are needed for US emission controls.

Sent from my Galaxy S3.