balance / timing chain gear out of sync

[Agent Orange]

I've had my 2.0T auto for about a year, 2009, 80k. Started to notice a rough idle when cold a few months ago. Got worse over the last few weeks to a point now where it has a real bad miss fire until it warms up and also seems to fluctuate power when normal driving and flatspots about 4k when I give it some stick. No error codes when taken to dealer. Changed plugs, cleaned fuel lines, changed IAT, checked MAF, checked vacuum leaks - desperate took to dealer yesterday and he thinks it's mechanical, timing chain/balance chain tension/gear not operating properly. car running -7% lean although I' m sure it's spitting out fuel when cold. He thinks this is ecu trying to compensate until warm. Quoted about £650 to replace gear, but about half if just balance pulley?? Dealer has a good reputation and I think the diagnosis makes sense, but need a second opinion before I book it in??

[Max Headroom]

Hello Agent Orange and welcome to the forums.

Sorry to hear of your bother. Only the other week I had a similar(ish) problem on a Vauxhall Meriva which was running like rubbish on start. Eventually during a cold snap it wouldn't start at all.
This turned out to be the coolant temperature switch/sender sending duff information to the ecu. The guage read okay!
I changed  it (£12) for a new one, and car now starts and runs fine.

[sgould]

Welcome!

I thought that the timing gear problem had been fixed.  On the early cars the guides could break.

I would wonder why a timing problem changes with the temperature of the engine.  Do you have any error codes?  I would be looking at the plugs and the ignition cassettes for a misfire.  But there are people on here who have more direct experience of these cars and their faults.

[Audax]

I'd start with replacing the thermostat and coolant temperature sensor. If it only does it when warming up then it suggests it has a problem with something during warm up cycle on the ecu rather than a mechanical problem.

[Agent Orange]

Thanks so far, but miss fire is only apparent when flat cold and disappears under load or when warm(er). No error codes and tried different plugs. Significant flat spot under hard acceleration at about 4k?

[Audax]

Does it not do this when started from hot? If so I'd really be pointing at thermostat and coolant temp sensor or possibly an oxygen sensor. I don't see how it could be timing gear given the description, if the timing is poor then it will always be poor. My experience with 9-5's where the timing is even 1 tooth out on the chain is that it will run fine at idle as the injectors and spark can compensate but under load they can't, that's the opposite of what you're describing.

[Agent Orange]

Don' t think its the coolant or O2 sensor as it's got progressively worse and didn't show any emission faults during it's MOT a few weeks ago. Also not sure why this would have it running lean?Gonna bite the bullet and take it in for them to strip down the pulley end to see if there is a problem with the timing.

[Audax]

Don' t think its the coolant or O2 sensor as it's got progressively worse and didn't show any emission faults during it's MOT a few weeks ago. Also not sure why this would have it running lean?Gonna bite the bullet and take it in for them to strip down the pulley end to see if there is a problem with the timing.

MOT is done when the engine is hot... I've known a 9-5 with a failed catalytic converter pass an MOT with the check engine light on. The MOT limits are way way outside the Saab limits. It's your money but for the cost of a coolant temp sensor I'd suggest having the chains stripped down is a bad idea.

[Max Headroom]

Don' t think its the coolant or O2 sensor as it's got progressively worse

That's exactly what happened to the Vauxhall I had the temp sensor fail on.
It got steadily worse until the point that it just would not start.

[Audax]

That's exactly what happened to the Vauxhall I had the temp sensor fail on.
It got steadily worse until the point tha it just would not start.

That's the other point I forgot to make, I've only ever known a bad o2 sensor to have failed gradually, pretty much the same thing with coolant temp sensors too.

[Agent Orange]

Good point - there's a smell as well when it starts, just checked again when it cooled down - definatly hydrocarbon type smell, maybe not petrol but must be coming from exhaust? Do you think running lean and intermittent power could be oxygen sensor or coolant sensor and wouldn't engine light be on or error code? Thanks

[Max Headroom]

Do you think running lean and intermittent power could be oxygen sensor or coolant sensor and wouldn't engine light be on or error code?

More information to try and help with your diagnosis:
I only got the error code on the Vauxhall when the temp sensor finally gave up completely. When it happened, it also put the cooling fan on permanently (- not exactly helpful when trying to start a cold engine!) which I guess was a 'failsafe' system trying to protect the engine, believing it to be an overtemp.

For the minimal cost of the price of a temp switch I would just change it. It is literally a10 minute job (depending on access) but make sure you have a long-reach socket or box spanner if it has a plug-type connection on it.
Oddly the replacement Vauxhall part was a different size hex to the replacement, which held me up as I had to locate another box-spanner to fit.

[Agent Orange]

I'll get one on order today and fit before the weekend - with the smell I mentioned yesterday I'll get the oxygen sensor at the same time.
Thanks

[sgould]

There are two oxygen sensors.  One each side of the catalytic convertor.  But they are not cheap. 

Trial and error can get expensive!

[Agent Orange]

Tell me about it! - 've also started to suspect my fuel filter may need looking at seeing another post - I'm always running down to the dregs. Could this be part of it?? Is it a seperate filter and easy to get at?