JTS sometimes idles on three cylinders
My 2.0 JTS sometimes idles like it's runnin' on three cylinders. Sometimes i'm feeling lack of pull on around 2000 rpm. I have had also misfire error in cylinder two twice on cold engine.
I've changed spark plugs and checked everything I could through Examiner Smart and after that using Bosch program. Contacts, coils phases, timing, etc. None errors are found.
Car is done ~55K miles.
The main problem is "sometimes", I cannot identify the reason why car sometimes behaves oddly and why sometimes it's running very nice and idle is quite smooth.
Please help me to identify this fault.
2004 - 156 2.0 16V JTS Turismo Internazionale
2008 - 159 3.2 24V JTS Q4 Q-tronic