1.8t 3000 rpm rattle and stutter

[Ro55_rsn]

Hi guys, my first post so hoping to find some helpful advice here.

So my 1.8t AUQ has been having this slight misfire on idle recently, only bouncing slight and you can hear it more standing by the exhaust. It sounds like it drops for a second every so often. But the most noticeable is the stutter when driving.
When i get to about 3k, it has this weird lagging feeling, where it lags for a few seconds and then eventually drives through the lag. But at the same time as it hits 3k, i have this weird rattle/squealing sound.

I've just put the 2.0 red coilpacks and new spark plugs in and still no difference. I unplugged the MAF and drove and still made no difference.
Smoke tested and no leaks.

So far it's stage 1 map, ramair induction and turbo back with decat.

Any help will be greatly appreciated.
Ross

 

[mty12345]

Not sure about the rattling noise but the hesitation could be lots of things. First thing to do is to check over all of the PCV and small pipework around the inlet manifold. Splits there are very common and can cause lumpy idle and hesitation. I know you said you smoke tested, but get in there with a torch and give the hoses a squeeze etc. Sometimes those pipes have splits that only open up under full boost pressure and won't always leak smoke from a smoke test. Also check the pipework that comes and goes to the N75 valve (electronic boost control) and maybe check that your DV valve isn't sticking also.

If you find nothing then you really need some data logs, (VCDS preferably) as these are complicated engines and you just end up replacing random expensive parts otherwise. Things to log are LTFT,STFT, boost pressure, O2/lambda, RPM. ignition timing. If you can do a pull from 2000rpm to 5500rpm in 3rd gear, that gives the best data. Post them up here and I will have a look for you.

If no logs then a video of the squealing sound may help

 

[Alex667]

I had a similar thing on my old 2008 Astra - it would idle, then drop a few hundred rpms at it seemed to miss then back to a stable idle and repeat. It was the breather value which was part of the valve cover itself, this was sticking causing a vacuum. Appreciate that's an NA car, but symptoms are similar... Would be worth checking.