Rough idle, failed to start once

[awns729]

I have a occasional stutter on a cold idle when starting the car and slight RPM fluctuation (dips and comes back but never even comes close to stalling), so I'm assuming based on these 2 symptoms there's a misfire going on. When I've had misfire codes in the past due to coils/plugs, I've seen similar symptoms but this time no codes when checking via cobb. This issue started right after warranty turbo replacement due to wastegate rattle.

Also, for the first time ever today, the car didn't start (even though I had driven it 2 hours prior so it wasn't cold). I had it in accessory mode for 10-15 minutes, and then went to start it. It tried to crank but failed, then I pushed the button immediately after that, and it started up and ran just fine (not even a rough idle). No codes again.

The car is fully stock at the moment b/c of recent turbo replacement, so none of this is mod related. Today, it felt normal on the highway, but a couple days ago it felt like it *may* have been stuttering a bit in 3rd and 4th gear pulls.

The 2 issues might not be related, but I wanted to mention everything. Things that I've done within the past 20k:

• OEM battery
• walnut blasting/carbon cleaning
• OEM plugs (from dealer)
• 6 OEM coils (FCP Euro)
• new turbos under warranty (the rough idle issue started right after this, and I'm down half a quart in 600 miles, which is more than normal since usually its a quart in 6000-7000 miles)

Not recently:

• hpfp replaced (obviously) in 2011, and some injectors (not sure how many)

So to sum up:
All issues started after turbo replacement (not sure if that's the cause though)
Consistent Idle fluctuation/stutter on cold starts
Didn't start one time after being in accessory mode for some time min, but started up right after. Only ever happened once.
More oil consumption after new turbos (still waiting to see if this is just a fluke or consistently more consumption)

I think one possibility is a leaky injector because that's the next typical thing to go wrong after fresh coils/plugs that'll cause a misfire. And based on the car not starting issue - I've heard the HPFP is pressurized as soon as you get in, and if my injector was leaking while I was sitting in the car for 10 minutes before hand, the fuel pressure might drop in that time due to the leaky injector and the cylinder might have some extra fuel in it, while other cylinders aren't getting enough fuel, and maybe that was the cause of the failed start attempt? It also explains the rough idle. Is this a valid theory?

How would you start troubleshooting this? Thanks!

[awns729]

hi guys

[edisapimp]

Hey, sorry we missed your post.

As for the more troubling issue of the car not starting, could you be more specific with what you mean when you said "It tried to crank but failed" ?

Do you mean you had a long crank and the car never turned over? I know you said the HPFP was replaced in 2011, but that is a classic symptom of a bad HPFP (the long cranks). Is this the only time that that has ever happened to you?

I will tell you that no one's N54 (especially modded) idles super smoothly. It's just not a smooth idling engine. When I drive my E46, I forget that it's even ON because of how quiet it is compared to my 1er. I will say that it seems you've addressed the most common issues (plugs/coils). Poor idle can also be a result of issues with the vacuum lines. There are some very common places that the vacuum lines can become frayed and/or broken. If you search N54 vacuum leak, you can find some diagrams that will point out to you where the weakest places are. Could save you some heartache and money.

If you are looking to start to diagnose, it's always best to start with the cheapest and simplest things first - so I would suggest driving the car until the tank is almost empty, then filling up with good quality 93octane fuel from a reputable gas station. Shitty gas can do weird things. After that, I would maybe try new plugs, and then go from there. My instinct is telling me that the non-starting issue could be the fuel pump. That's my non-expert opinion. Good luck and Happy Motoring.

[awns729]

Originally Posted by edisapimp

Hey, sorry we missed your post.

As for the more troubling issue of the car not starting, could you be more specific with what you mean when you said "It tried to crank but failed" ?

Do you mean you had a long crank and the car never turned over? I know you said the HPFP was replaced in 2011, but that is a classic symptom of a bad HPFP (the long cranks). Is this the only time that that has ever happened to you?

I will tell you that no one's N54 (especially modded) idles super smoothly. It's just not a smooth idling engine. When I drive my E46, I forget that it's even ON because of how quiet it is compared to my 1er. I will say that it seems you've addressed the most common issues (plugs/coils). Poor idle can also be a result of issues with the vacuum lines. There are some very common places that the vacuum lines can become frayed and/or broken. If you search N54 vacuum leak, you can find some diagrams that will point out to you where the weakest places are. Could save you some heartache and money.

If you are looking to start to diagnose, it's always best to start with the cheapest and simplest things first - so I would suggest driving the car until the tank is almost empty, then filling up with good quality 93octane fuel from a reputable gas station. Shitty gas can do weird things. After that, I would maybe try new plugs, and then go from there. My instinct is telling me that the non-starting issue could be the fuel pump. That's my non-expert opinion. Good luck and Happy Motoring.

No worries!

Yes, it cranked and never turned over. It didn't sound like a huge struggle while it was cranking and it didn't seem to crank for too long, maybe a few seconds (not like the HPFP failure videos I've seen on youtube). But yes, I've had 0 issues cranking besides that 1 time when it was on in accessory mode for 10 minutes before (which is how I came up with my primed fuel pump + leaky injector causing the failed crank theory).

I've had the car for 3 years, and this rough idle issue is similar to other idle issues I've had that have eventually lead to misfire codes, so while I understand what you mean about never having a smooth idle, it's fluctuating much more than normal these days, so I feel like something must be off.

Thanks for the vacuum line advice - I'll do some googling on that.

At this point, I've gone through many tanks from the typical gas stations I go to, so I'm feeling like I can start to rule out bad gas, but I'll continue to be diligent about it for the next few weeks.

I guess I'll do some digging on the vacuum lines and give this another week or two to see if i can get a code to pop up.

Thanks for your help!