Greetings all skoda oweners, I hope I am in the correct subsection, if not, then please moderators move the topic to the correct one.

Car is 2008/12 Octavia with 1.8 tsi CDAA engine and my problem is lumpy idle (i have searched and read almost every topic I have found on the internet but I haven't got a answer for my problem). I also know here is basically the same topic but the problem was different. Mileage is under 100 000km/60 000 miles.

The problem is following, SOMETIMES the car's idle is a little bit jumpy, it doesn't happen all the time and sometimes it has bigger lumps and sometimes smaller ones, two mechanics have diagnosed this problem with no final result. I wouldn't actually mind the problem but it gives me CEL. Trouble codes are P0171 system too lean and also intake system air leak (I can tell the code in the evening). It is possible to clear the codes but they come back (about a day driving). Also car gives CEL a little while later than the codes appear.

We have changed PCV valve, diverter valve, sparkplugs, PCV hose (tube), intercooler gasgets, both O2 sensors (the front and the rear), MAF sensor and still no result. I just visited my dealer who diagnosed intercooler gasgets and PCV hose (very little air leaks) and thought that with perfectly good readings O2 sensor might be faulty, OK changed them all but no result.

Maybe there are more common problems that we don't know about? I don't want to just throw parts at it anymore. Help needed badly.

What readings are you getting for fuel pressure regulation?.

How to check that? Last when I visited my dealer they also said that all the readings from the engine are OK. But I can recheck them.

OK new error code - P119A fuel pressor sensor incorrect. After googling a bit I found out that the sensor itself may not be the problem. There were suggestions about in tank fuel lift pump. Any comments?

Or the high pressure pump on the engine. 

Can they be diagnosed correctly? Just don't want to throw parts at it anymore. Which is the most common to fail?

Check fuel rail pressure. If it's constantly at around 5-10 bar even when revved then the high pressure pump is at fault as it should be much higher (around 45-50 bar).

1 minute ago, James@RRGRochdale said:

Check fuel rail pressure. If it's constantly at around 5-10 bar even when revved then the high pressure pump is at fault as it should be much higher (around 45-50 bar).

Thank you! Will check that.

Rail pressure is OK. When revved then it`s around 45-50 bar and when idle then under 40, around 38-39. What next? :S

Try some decent fuel,

vpower or whatever and/or additive and give it a damn good run?

What fuel do you use?