GTI intermittent stutter/misfires

[Hevoshullu]

Hello everyone and sorry for starting another thread on the subject but I didn't really find anything related nor solved ones.

Thing is, my 2007 GTI started getting occasional misfires/stuttering on low rpm / light throttle a week back. Car also lit up the CEL light. They are kind of like single jerks of a cylinder not firing properly. Under acceleration everything is fine though. First thing I thought was the coilpacks but the original faulty ones have been replaced in 2011 under VW warranty. I put in new spark plugs a year ago too.

I just got my car back from my local VAG expert and the only thing they found was a faulty thermostat and a fault code P0100 referring to a voltage problem in the mass air flow sensor (MAF). They tried fitting in a new MAF unit but it didn't solve the problem. The same fault code along with the misfires came back regardless of the new MAF unit. I booked a time next week to inspect the fault further and to replace the thermostat.

Do you guys have any ideas what could cause this? It definitely seems like an electrical issue maybe in corroded wiring or perhaps the replaced coil packs are the problem? Maybe the injectors or coked inlet manifold?

Any help is greatly appreciated!

Best regards,
Lauri from Finland

[cooljimy84]

The steps i did to test mine were the following, some are optional....

Swap the spark plug from the cylinder misfireing with another, see if fault follows using a scan tool (Vagcom, or other that can detect misfires live)
Swap the coil pack from the cylinder misfireing with another, see if fault follows.
Give it the beans (safely) hit the rev limiter.
Drive a few junctions on the M25 at 5,000 rpm. (it then didn't do it for ages)
I then got the thermostat and HPFP cam follower (as i was not hitting 90 while driving, and the follower had never been changed)
FIX....

She does still have a misfire or two once, maybe twice a week, but nothing like she was....

[Hevoshullu]

It appears that the cause of my misfires has been in corroded wirings linked to the ECU. My local garage did some measuring and cleaning up with them and the car hasn't had a misfire since. *knocking on wood*

[cooljimy84]

Kool, did they find what has leaking on to the wires ?

[Hevoshullu]

Actually the whole wire going from MAF to the ECU was split in half from a tight twist. It was repaired and the car hasn't missed a beat since!