Starting to regret my purchase...

[RyanS96]

I recently bought a 2012 MS3 and it ran great for the first week... 58K miles, last owner did HPFP, Vibrant FMIC, CS TIP, CS intake (HKS filter idk why), 3.5in turbo back straight pipe, HKS BOV, APV3 with an OTS tune. I've been chasing P0300 for a few weeks now. Cleaned intake valves (didn't do it with walnut media ~6 hour soak in top engine cleaner and a scrape), manifold, TB. No CEL for like 3-4 days after that but it came back. Ran some fuel injector cleaner through yesterday but haven't gone through much since I'm not driving it a lot. Did plugs today NGK 6510 gapped to .026. Last thing I did after a short drive today that gave another misfire was cleaned the MAF. Now it seems to run lean after letting off the throttle. It will go up to 17-18 then right back down to 14.8. Didn't misfire but I don't want to drive it now since the AFR seems lean. I should do a compression test but I'm afraid of bad news since I just bought it....... Any suggestions? I know I need a pro tune but I want to get the misfire figured out first.

[Db09ms3]

Keep investigating, you're on a good start. Compression test will tell you more, don't be skerrd.

[Jeff23spl]

if it keep 17-18 when you let off throttle, i would give a look at a leaking injector....it should fall off completely lean at 29-30 AFR when you completely let off after loading it a bit and return back to stoich as soon as you touche the throttle again...

That could mean there is still fuel coming in even if the ECU is calling 0 IDC. And accumulated fuel when you start the car makes missfire....

Check engine compression too.

Before shuting off the car, check fuel pressure to be in the 450 range and if you shut it down and turn the key back to ignition position to power up the AP, you should be reading a fuel pressure increase above 1500psi and stay there for a while because fuel is supposed to be in a sealed place. If it drops quickly, you have something there.

[RyanS96]

Did a compression test today. 180 on all 4 super glad that came out great. Gonna get my injectors cleaned and tested on my next days off.

[Jeff23spl]

Originally Posted by RyanS96 Did a compression test today. 180 on all 4 super glad that came out great. Gonna get my injectors cleaned and tested on my next days off.

these 1700psi injectors would need new seals, so you may read about few threads....

Diesel shop can usually clean them or SP3performance can do it too but it means downtime...

[RyanS96]

I was thinking about that too. Why are they so expensive though. Is the material they're made out of super pricey? Might as well do an egr delete while I'm down there.

[Jeff23spl]

if you don't have smoke test every year to pass, yes egr delete is the way to go. You just need something to cap where the pipe goes.
The kits aren't expensive but i have made my own with a metal plate at the valve side and used the manifold ends as an extra port with a reducer for a boost gage....

[RyanS96]

So since my last reply I've pulled the injectors and got them cleaned and tested. All 4 o rings and corksport seals were installed. EGR delete was done, sill misfiring. Whats drives me crazy is the week before I did the seals, no misfire!!!! After i got the car up and running I did a small pull and now its back to throwing p0300 multiple times during a short drive. I feel like I just need a tune but I wanted the key issues sorted out before I paid for that. Is it safe to say that is my next step? I live by English Racing and i was gonna bring my car to them when I get paid but I'd rather not spend hours on the dyno and money on parts to get it running right, I cant afford that :/.