Car has come from another garage with a new AMM, it also had new coils which didn't help so originals were refitted.

This issue is a very rough/lumpy idle almost to stalling which is intermittent but does seem worse when hot. The P codes have not logged since we have had it.

First thoughts were an intake leak so smoked inlet and found nothing? Also scoped cam and crank which do not change during rough or good idle condition, also checked fuel pressure serially which appears fine. It has had some previous head work apparently before the customer bought the car which pushed us towards a possible timing issue hence scoping of the cam/crank but no syn codes. Also when it's running rough it pops back through the air box.

No other actual values are jumping out at us? Fuel trim seems fine (4% total)
Interestingly when you unplug the AMM the fault clears? (Obviously the reason it was replaced) So still think possible air intake calculation issue? Have heard of these suffering from the breather systems but unfamiliar with these issues myself? Not sure which way to go next with this one, any ideas welcome??

Thanks for reading

Hi Luke,

Have you monitored the misfire counters under fault conditions ?

Regards

Glyn

Thanks for speedy reply,
sorry meant to say that it does intermittently register a cylinder 1 misfire (very rarely and only once)
But the misfire monitor is disabled as the symptom occurs? Read with vag com and autocom and both say enabled running well then disabled when fault starts??

hi luke

has this problem started after the head work?
or was the head work done because of the problem?

peter

Unfortunately this is not known, the customer bought the car with the issue and only found out about the head work once the original garage asked him to go back through his paperwork where he found "cylinder valve damage"

Apparently no more info than this I'm afraid?? This is what had us thinking timing.
I checked the physical timing today using the top mark and the lower mark on the timing belt cover and the auxiliary drive belt pulley which shows it's possibly a tooth out? How accurate is that lower mark though? Don't want to needlessly pull it apart? And would a timing issue not be constant??

Thanks for the replies

Just to add started it from cold to bring the vehicle in for the night and it was running terribly and felt like a definite misfire and obvious popping back through the intake.

Luke check the none return valve in the breather on top of the manifold, the flap breaks loose inside, so a smoke test will not show up the air leak as it is from the crank case to the manifold,
then reset the fuel adaption
Tom

hi luke
had exactly same symptoms even down to head being refurbished not by us and popping back through inlet manifold when cold, after lots of testing we did a relative compression test using pico when cold, as missfire only happened for two/three minutes of starting from cold after that was ok, we found one cylinder down, removed head and found valve springs on that one cylinder had been compressed, presumably from belt letting go, replaced and happy days.
Not saying this is your fault but worth bearing in mind.

peter

Thanks for your reply peter deffinetley something I will consider and eliminate if I can.

Which breather one way valve are you speaking of Tom? As I can remember the only breather pipe work in the manifold area are two plastic corrugated hoses going into either end of the cylinder head cover? It might be worth mentioning that this engine is naturally aspirated.

As I said i am aware that these engines apparently suffer with breather valve issues but would this not log "system lean fault codes" ?
Sorry if I seem argumentative but just trying to get my noodle around how these different faults which your all suggesting might affect the running, I'm more interested in learning through this job than fixing it now, although I will try my best
Thanks for the relies keep them coming!!

On a side note does anyone have any info on exactly how these breather systems actually operate? Spent about a month reading up on the PSA's but am all the wiser for it

UPDATE-

Got back on this one again at last (hectic few days)
I am leaning towards the internal air leak theory with this as if when the vehicle is running smooth you remove the oil filler cap it induces the exact same symptoms, even down to clearing up when the air mass plug is removed (with the cap still off)

So clearly an air calculation issue and not timing. Any pointers on where this is likely to be?

Will update if anything is found.

Thanks again

Crank case breather valve.

Thanks Chris exactly what I was thinking, where is it situated on this engine as it dosent have the regular unit which bolts to the rocker cover?

I suspect it is actually part of the cover itself as there is what looks like a moulded valve within it which has a rubber diaphragm inside.

Am I right in believing this diaphram should only allow flow in one direction like the other types?? This one allows flow both ways so I am thinking this could be our problem but at £120 +vat I'd like to be sure I'm unsure of its purpose what with this being non turbo and if failure of this valve could even cause this issue on this engine?

a good description of the breather etc and what happens if it is broken

http://www.vaglinks.com/docs/vw/misc/vw.com_2.0l_fsi_turbo_ssp_821503.pdf

Eventually narrowed it down to an injector fault after the vehicle developed a very smokey start up (raw un-burnt fuel)
left vehicle overnight and checked hydrocarbons in the cylinders and found highly elevated levels in three cylinders.
Upon stripping to replace injectors we found the variable tract intake flaps were missing (broken) obviously the original cause of the engine damage. Customer went ahead with the replacement of all 4 injectors and the motor/flap unit. All good since
thanks for the replies.
How crucial are those flaps to the running of the vehicle? could it have been causing idling issues as well as the dripping injectors?

Does this help,

www.volkspage.net/technik/ssp/ssp/SSP_296_d1.pdf