Rough idle (misfire, rev fluctuations), rough driving (plz help)
Hey guys 🤙🏻
Had my mk6 gti for quite some time now. Got into my car after work and something seemed off, engine revved slightly higher than normal after turning over on cold start. Once its 'cold start' period finished, revs dropped but starting misfiring as it happened. Doesn't misfire while driving though, only when stationary and not up to temperature, once up to temperature misfire goes away.
The car does not throw up any engine lights at all.
Another thing also is the revs fluctuate on idle when not misfiring, revving up slowly to 1.5k-1.8k then drops slightly and repeats. Also does this when I am changing gears, revs sit high for a second until I let out the clutch (manual) even though I am not on the accelerator. My stage is stage 2 tuned, and burbles under deceleration, although it does not do this anymore as if the cars accelerator is stuck slightly open or is broken. 🤷
Also makes very highly pitched noise from engine both driving and idle. Have been looked at by mechanic, is apparently not a vacuum leak, and have reset codes and modules after plugging in an expensive code reader on some fancy software (forgotten the name mechanic told me) although had not make a difference.
Mechanic tested if it was a pcv valve fail, he claims it is all working and unrelated to the problem.
Possible problems (imo)
Faulty fuel injector
Needing carbon clean out
Things to note:
167,000km
Maintenance: Timing chain, water pump, oil pump, upgraded plugs and coils (9,000km ago), recent service.
Mods: intake, d/p, exhaust, fmic, d/v, stage 2 tune.
I apologise for such a yap, I really do love this car and would like to provide as much detail as I can so hopefully you guys can give suggestions 🙏
Can show more videos to help