Hi everyone, just thought I would say hi to everyone with a series of problems i've got, hopefully i'll manage to glean some technical information from some of you..

First of all, it's for a 2006 VW Polo 1.2 - It has recently reached 70,000 miles

I have recently purchased a snap on microscan to troubleshoot my Engine management light and it came up with a few codes, they were the following:-

16804 (P0420) - Catalyst system bank 1 operation below threshold - intermittent

16556 (P0172) - Fuel trim bank 1 system too rich

16556 (P0172) - Fuel trim bank 1 system too rich - intermittent

16685 (P0301) - Cylinder 1 misfire detected - Intermittent

16686 (P0302) - Cylinder 2 misfire detected - Intermittent

16687 (P0303) - Cylinder 3 misfire detected - Intermittent

16684 (P0300) - Random/Multiple cylinder misfire detected - Intermittent

Now I have replaced the individual coil packs (all three) and spark plugs and it seems to be running a little bit smoother, I have cleared the codes now and they haven't reappeared in 50 miles or so but it is not very stable at idle, it seems to struggle when the air con is on and nearly stalls.

Is there anything that is common to all of these faults at all, or could it be that stupidly before I checked the codes I cleaned all the electrical connections in the engine bay with an electrical cleaner and this has caused the fault codes? I could be on completely the wrong track if that is the case and god knows what is causing the rough running. I have since put a bit of redex in the petrol tank today to see whether the injectors may have been blocked, it seems not as it's still running poorly..

Any help would be much appreciated.

May be a faulty lambda sensor

It may pay to check for vacuum leaks, as if there are any, these will make themselves known at idle speed.

This may be controversial, but I would treat it to a couple of tanks full of Shell V-Power, I find that, although it is a bit expensive, it does what it claims to do - the engine runs far smoother, seems to give more power (more torque to be exact) and I also get better fuel consumption figures when using this. It is not however, a cure for all ills.

The only other thing that you can do, is keep checking for fault codes.

It is of course possible that the fault codes which you have now cleared, related to an earlier problem that was overcome previously.

Regards.

Hi again,

OK since I was last on I have checked for vac leaks, none found, i've put through a tank or so of decent fuel, i've also replaced the Pre Cat O2 sensor as I thought this could be the problem. I've taken the car for a drive today to see how it was driving and it's still rough, stalling at idle worse than ever, when I pulled onto the drive I got another code, and that was P0303 - Cylinder 3 misfire detected. Now would you suggest checking the belt to see if it's jumped a tooth or is the next step a compression test? Thanks, thinking I should've taken it to a garage as it's costing a fortune..

Compression test, quite common for head problems.

Also it's a chain not a belt dude.

Compression test, quite common for head problems.

Also it's a chain not a belt dude.

Nice one,thanks bud.. Will come back with results.

Compression test, quite common for head problems.

Also it's a chain not a belt dude.

Right, i've done a compression test now and the results are as follows

Cylinder # 1 is 198psi

Cylinder # 2 is 195 psi

Cylinder # 3 is 120psi

Bad results i figure for #3 but what is the next step?

And how much will it cost for parts etc?

Thanks

My money is on a burnt out valve seat on cylinder 3. Head off job I reckon.

How ever drop a bit of oil down cylinder 3 and see if the compression rises if it does this would indicate piston or bore problems - from what I've seen this is unlikely tho.

My money is on a burnt out valve seat on cylinder 3. Head off job I reckon.

How ever drop a bit of oil down cylinder 3 and see if the compression rises if it does this would indicate piston or bore problems - from what I've seen this is unlikely tho.

Thanks mate,

Just done the compression test again and as you suggested it did not rise with a bit of oil down into cylinder 3..

Is the job a big job or not, i'm happy to give it a go, just don't want to pay extortionate fees, i'm an aircraft engineer by trade, completely different I know, but what could possibly go wrong?

How much am I looking at for all the parts / what parts do I need?

Thanks very much

Um your an engineer so you shouldn't find it too bad the biggest arse would be the timing chains, but have a search an you will find enough guides and information about how to do them on google pm me if you need anything off elsapro (VAG workshop manual)

As for parts, you will need gaskets and I'd put new chains and tensioners aswell.

And you could either recut the valve seats yourself, but personally I'd just take it to a machine shop and have them do it, they will also inspect the head, skim an pressure test as well.

And off topic but do aircraft engineers use imperial or metric.

And off topic but do aircraft engineers use imperial or metric.

Imperial but I seem to remember the IAE V2500 on the A320 did have some metric as the gearbox was made by Fiat!!! might be wrong been a good few years since I worked on them

Ah right I thought some one was having me off lol

Let us know how you get on buddy.