Surely someone must know?

[Deano2711]

Try getting it hooked up to a Vag Com cable or fault code reader. Vag Com available off E.Bay for around a tenner. Faulty sensors etc will come up with a fault code in most cases. May help in the long run.

[harlemex]

try disconnecting your maf sensor plug.

[Christo77]

Remember the cambelt is toothed, would have to be worryingly slack to be able to slip..or the tensioner has failed.
But, you can easilly check that and check that the timing marks line up, if that's all ok then well..it's guessing from here really.

As said already by others the coil would have been my first shout also, as you seem to think that's alright then you just gotta get back to basics and check the obvious things first.
From the items you mentioned already there's other things like fuel/ecu relays, MAF sensor, Hall sender..have you checked breather and vaccum lines..

[james42]

i`ve been looking at jbh`s car today. found the timing belt slightly loose. removed no1 spark and determined tdc with proding device, marks on cam pulley did not align with the mark on the head.it was about 5 teeth out. re set cam but no difference.good spark and petrol arriving at chamber. spark will ignite mixture with spark plug held at open spark plug hole. apparently no valve crunching noises were heard initially and there are none now. i`m thinking compression test next,if good compression that means the valves are seating nicely, right? tried with mass air disconnected.tried to remove throttle potentiometer but it was keen to stay where it was. i`m keen not to create a secondary issue by breaking it. code reader sounds a sensible move. other than the valves is there anything that could be damaged by the belt jumping?

[Christo77]

If the cambelt has managed to jump out of it's toothing on the pulleys then that's quite a concern and who knows how far round it's actually travelled!
If a belt has been subjected to even very slight damage or just purely suspect about it's age/condition then it should be replaced period.
If the thing has jumped round then the toothing may well be damaged and must be discarded!
Also you'll need to check the pulleys for integrity including the tensioner and that ideally in this case should be replaced too..

All that asside, the first thing though is a check on the cylinder head/valves for damage, ie with your compression test i guess..

[Wayne]

Sounds like it has lost compression

[Dubbyboy]

This may sound completely numpty like, but I had a similar experience the other morning.
Parked up the night before, not a hint of an issue, following morning not even a hint it would fire up.
Tried allsorts, then tried something my in-law does when he starts his car.
Put my foot on the throttle half way down (I know it's injection and shouldn't need to) and I got a splutter from the engine.
Stopped then planted my throttle to the floor (with all the turning over I knew there was oil pressure by now) and the thing burst into life.
Ran a bit ropey at first then cleared itself, touch wood hasn't happened since.

It's at least worth a try, won't cost anything.

[jbh39]

Thought I had better conclude this.....turns out when I turned the engine off, the timing belt HAD slipped. Very lucky it hadnt messed the valves up! Managed to sort it out.....................phew.

[Christo77]

Well nice one..indeed your lucky!  You haven't re used the old belt i hope..

[thai-wronghorse]

What made you suspect a slipped cambelt?