Intermittant MISFIRE?? Audi a3 1.4 TFSI 2010

[MikesTractor]

NEED HELP. Very annoying problem. Not just any common misfire.

I started having misfires when I bought the car 8 months ago.
The misfire happened when the car reached 30mph and above. Like any good samaritan with a 2nd hand car without maintenance history, I changed spark plugs which cured the problem.
A couple months go by and problem re-introduces itself. Needing a car service anyways, I took the car to a local garage and asked if they could change spark plugs again and make the missfire go away. They said it was cylinder 2 and 4. The missfire went away but only for 10 Miles! They recommended I change coil packs next, which I did, but that didn't cure the problem at all. Thinking it could be a fuel problem I aslo poured injector cleaner in the tank but it only started misfiring worse.

I was fed up chasing the issue myself as I needed a functioning car for work, so took it to an Audi garage. They performed a £204 full diagnostics and here is what they found out:
Missfire on Cylinder 2 and 4, swapped sparkplugs to 1 and 3, now missfire on 1 and 3. So, easy fix, they blamed the "non genuine Audi" spark plugs and put in new Audi ones. The problem was gone and they performed a full drive test which went successfully. I got the car back and this time after 250 miles I started having misfirings again??
I just started a week of work and needed the car so, I couldn't bring it in (luckily I mostly commuted in 20mph zones so it barely missfired). When I topped up the car with fuel mid-week I decided to fill it up with e5 Super 98 as a small attempt to help fix it. To my surpise after about 50 miles of driving with 98 in my car, the missfiring went away completely! It ran great, but it only made me more confused what the problem was. HOWEVER, I'm now 300 miles further, my tank is half full still with the super 98, and I'm having misfiring again. It's not a constant misfiring cylinder, its sporadic; going up hills, or when accelerating over 30 mph.

I've yet to do a cylinder pressure test myself as I'm not sure Audi did it. I'm inclined to just replace the sparkplugs again with expensive ones but it's just asking for the problem to come back; if it goes away at all. Not sure what to do! Anyone who knows more about engines could have an idea what could cause these symptoms?? Could it be burnt valves? Bad injectors? electric fault? clueless.

From previous threads with similar issues, here are some common questions. My car doesn't have Cylinder on Demand. turbo got looked at recently by Audi regarding a sensor fault so, unlikely its a boost issue. Car has 114k miles. Old but definitely not hopeless

On a side note, just in case it might be related, my coolant runs out quite frequently and have to top it up. I checked the engine oil cap and there's no fouled oil (garage also didn't notice bad oil when I took it in for service), nor am I getting white smoke out of the exhaust. Pipes seem ok and never have a puddle under my car after standing still for long time.

I'd love to rely on my car for work and travel without filling the boot up with coolant and sparkplugs. Thanks in advance
Mike

 

[samuelh_888]

Injector cleaner is the work of the devil. It pushes more crap into the injector baskets so that will make the car run worse. You need to get your injectors ultrasonically cleaned and your plugs and coils replaced. Then get a compression test to check the head gasket hasn’t gone hence using water.
Do you know if the cambelt has been replaced as the water pump is typically replaced at the same time - that may be leaking but you’d notice this.

 

[MikesTractor]

Injector cleaner is the work of the devil. It pushes more crap into the injector baskets so that will make the car run worse. You need to get your injectors ultrasonically cleaned and your plugs and coils replaced. Then get a compression test to check the head gasket hasn’t gone hence using water.
Do you know if the cambelt has been replaced as the water pump is typically replaced at the same time - that may be leaking but you’d notice this.

Thanks for taking the time to reply.
Cam belt looks relatively new so am not worried about it. it would have flagged up with Audi if it wasn't. Good to know about the injector cleaner being rubbish. I wasn't able to find any success stories about it either so it was a cheap shot in the dark. I can see how the enjectors could be the issue here but I'm finding it hard to emagine why the misfiring followed the spark plugs when the Audi garage swapped them around. Surely it would have stayed with the same cylinder if it was an injector problem? I have complete set of coil packs ready to be swapped out, not cheap ones. Compression test will probably rule out 50% of possible issues so that's moved up on the priority list, just waiting to see mate who owns one to borrow it off him.

I've also been recommended to try an engine carbon cleaning service where they inject the cylinders with cleaning product. Anyone have experience with this service? worth it? in case the issue is carbon build up.

 

[samisnake]

there isnt a cambelt on this engine, its chain driven. the water pump runs off the aux/drive belt. my waterpump (2011 1.4) went last year @ around 80k. was weeping a little, but no enough to lose loads of coolant.

also do a pressure test on the cooling system. might be something simple like the coolant botle cap failing, or a loose hose, or something bigger like the rad leaking. headgaskets on these engines isnt a common issue, but never know. some leaks you wouldnt know from it being parked up, as they only appear under pressure.

not worth it for the cleaning. from the sounds of it, theyll inject a cleaner into the intake with the engine on (seafoam style cleaner). those dont really work. for an effective cleaning, the intake needs to be removed and manually cleaned eg. walnut blasting or hand scraping. again, not really a common issue on this particular engine.

 

[samuelh_888]

there isnt a cambelt on this engine, its chain driven. the water pump runs off the aux/drive belt. my waterpump (2011 1.4) went last year @ around 80k. was weeping a little, but no enough to lose loads of coolant.

also do a pressure test on the cooling system. might be something simple like the coolant botle cap failing, or a loose hose, or something bigger like the rad leaking. headgaskets on these engines isnt a common issue, but never know. some leaks you wouldnt know from it being parked up, as they only appear under pressure.

not worth it for the cleaning. from the sounds of it, theyll inject a cleaner into the intake with the engine on (seafoam style cleaner). those dont really work. for an effective cleaning, the intake needs to be removed and manually cleaned eg. walnut blasting or hand scraping. again, not really a common issue on this particular engine.

Sorry my bad, I was thinking S3 re cam belt - I should have read the title better!