2008 GT 2.0 TSi, rough idle and misfire

[SteveJJ]

I've a 2008 GT 2.0 TSi and it's just developed an engine fault. A couple of weeks ago the CEL came on and it was a "P0171 - System too lean (bank 1)" code. The tickover was also pretty rough. I looked into this and the most likely cause seemed to be the PCV valve. I replaced that, along with the front breather hose, but it hasn't solved the tickover problem. Apart from ticking over the car feels to be driving fine once it's going.

I took it for a drive and am now getting pending P0300, P0301, P0302, P0303, and P0304 codes - these are misfires on all cylinders. I took off the connectors to the coil packs, checked they were clean and re-seated them but that all seems to be fine. Prior to changing the PVC I hadn't seen these particular codes, just the P0171. It's still flagging a misfire across all cylinders.

I'm not sure if it's related but there is quite a vacuum on the oil filler cap and dipstick, at tickover then get sucked shut.

Is it possible the rough tickover is caused by something else and in changing the PCV I somehow also disrupted the ignition system?

Any thoughts on what to do next please?


(2019-08-20 18:45) Edited to add I've just disconnected the front breather hose and the tickover became very rough, barely keeping running. If I block the pipe to the inlet manifold then it went back to the current rough tickover. I suspect this means it isn’t the PCV valve.

[jtbrown]

Sounds like it could be the intake flapper motor. I had the same issue, you can self diagnose it quite easily. Hope this helps:
http://www.sciroccocentral.co.uk/forum/ ... 25&t=20099" onclick="window.open(this.href);return false;

[SteveJJ]

Thanks for that idea, I've just checked that and mine is seated OK.

I've not had any more of the P03nn codes but still get the P0171 every few hours of driving. I’m not using the car much at the moment but need to get back onto tracking the problem down. The tickover is still pretty rough, but not as bad as when the hose is opened. When driving it feels OK, possibly hesitates a little but drives smoothly.

The post at https://forums.vwvortex.com/showthread.php?4691554" onclick="window.open(this.href);return false; seems worth me working through next time I get an opportunity.

[pablocullen]

Hey, i had a few similar issues to this, took ages to figure it out!

Mine turned out to be the electrical connector on the throttle control body, previous owner recently had the throttle body replaced and the mechanic must have pulled really hard on the cables to get it the connector off, to fix it i pushed the cables back in so the pins connected more securely, havn't had any issues since. The correct way to do this job would be to cut the cables and resolder a new connector on which i vowed to do if it broke down again after my fix, its been running a couple months now without a re-occurance of the issue.

I also needed to clear all codes once i did the above for the rough idling to stop.

Hope this helps in some way.

[SteveJJ]

Thanks, I'll add those to the list of things to check.

[SteveJJ]

I’ve noticed a possibly pattern to when it happens. The CEL light with a P0171 code seems to usually come on when I’m braking, either manoeuvring or in motorway traffic. One of the posts I remember reading mentioned the brake servo vacuum hose as a possible case of the air leak problem. Next time I get under the bonnet I'll pay particular attention to that hose.

[SteveJJ]

I finally reached my diagnostic limits and took in into a garage who know these cars pretty well. They ran a few tests and concluded it was the engine rear main oil seal. They’ve replaced the seal and the car is now running beautifully. It’s quite possible the PCV valve I replaced in the summer had failed and that in turn caused the damage to the seal.

[Joshn2]

Did you ever get this problem solved ? I have the same codes

[SteveJJ]

Hi, yes it cleared up after the oil seal was replaced. I guess oil was getting into places it shouldn't have.