There are several variations on the 1.4 TSi problem, nothings singular either, take your choice .............
1) Faulty coil packs.
- Early Coil Packs which are not reliable replaced with units as per later standard fitted from mid 2009 onwards.
- Faulty batch of Coil Packs in Wk35/09.
2) Misfires - Injector part changed from Mar'10 onwards in production. To aid spray pattern and over come deposits restricting fuelling.
3) Misfires - Injector batch in last quarter of 2009 to be replaced on occurrence.
4) Misfires generally (carboning of cylinders and injectors) - ECU software updates for fuelling problems (Australia issue mentioned above ie. software G5859/G5860).
5) Warm-up misfires with low humidity & higher temperature present - ECU software fix expected soon
6) Erratic running with EG warning lamp - Stretching of cam timing chain at mileages above 20,000Km and some need for heat insulation on an oil feed pipe to the turbo plus other checks.
7) Mechanical free play in the engine leading to piston/ring failure.
8 ) Fuel rating/brand
link
I've read through here,
Most only report a fault(s), ie. misfires/loss of compression, not the cause. One remark is made about the new replacement engine not making noises like the old one.
Reports both mechanical freeplay in the engine and piston/ring or just piston/ring failure, more occurrances of the latter.
The point about the misfires is that in cases above 1, 2, 3, 4 & 5; it leads to fuel washing the lubricating oil from cylinder walls. Left long term this leads to the piston rings failing in the affected cylinder. And therefore loss of compression.
The misfires are not always apparent to the driver, they don't always switch on the dash EG lamp and don't always log a fault code in the engine ECU.
6 is different in that valve timing gets out of synch.
Some of the problem is coil packs failing (nothing new there with VW if you know Golf Mk4's & 5's), others its the injectors becoming blocked with carbon and other deposits and not spraying the fuel properly into the cylinder or the right quantity.
VW's solution for some time has been to change the ECU software. Current Scirocco engine ECU software (7th release) is identified as G5859 or G5860 (this is also the Australian update). This can be seen in the "Component" field on the Engine ECU screen in VCDS. This software changes during the warm-up phase the way the electric throttle works and limits the throttle opening to 70%ish until above a 5,000 rpm. It also changes the amount of fuelling as various stages of engine operation to compensate for the injector shortcomings to ensure combustion happens.
In the case of 5., there are engines that experience poor running and misfires when the humidity drops below 20% at certain temperatures. This happens when the engine is warming up with the coolant at about 35'C, ie. 2 to 4 minutes from cold starting the engine. This fault is still open with VW and there is no fix at present. The fix will be another ECU software update.
C.